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How to make a list of partial sums using forEach


Creating an array of cumulative sum in javascriptHow do JavaScript closures work?How do I check if an element is hidden in jQuery?jQuery get specific option tag textHow do I check if an array includes an object in JavaScript?How do I redirect to another webpage?How do I make the first letter of a string uppercase in JavaScript?How to check whether a string contains a substring in JavaScript?How do I remove a particular element from an array in JavaScript?Remove duplicate values from JS arrayHow does PHP 'foreach' actually work?













18















I have an array of arrays which looks like this:



changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];


I want to get the next value in the array by adding the last value



values = [ [1, 2, 3, 2], [1, 0, -1], [1, 2] ];


so far I have tried to use a forEach:



changes.forEach(change => 
let i = changes.indexOf(change);
let newValue = change[i] + change[i + 1]
);


I think I am on the right lines but I cannot get this approach to work, or maybe there is a better way to do it.










share|improve this question









New contributor




Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.















  • 1





    Please elaborate this "I want to be able to increment the values based on the next value in the array to get this result:"

    – Syed Mehtab Hassan
    Mar 20 at 10:51











  • I want to add the numbers in the array that are next to each other together to make the next number in the array

    – Team Cafe
    Mar 20 at 10:52






  • 1





    @JollyJoker Thomas simulate .reduce method, why not use .reduce directly ?

    – R3tep
    Mar 20 at 12:26






  • 1





    @Thomas Look my answer, you can use an array as accumulator.

    – R3tep
    Mar 20 at 12:52






  • 1





    Never use forEach if you want to produce a result.

    – Bergi
    Mar 20 at 13:55















18















I have an array of arrays which looks like this:



changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];


I want to get the next value in the array by adding the last value



values = [ [1, 2, 3, 2], [1, 0, -1], [1, 2] ];


so far I have tried to use a forEach:



changes.forEach(change => 
let i = changes.indexOf(change);
let newValue = change[i] + change[i + 1]
);


I think I am on the right lines but I cannot get this approach to work, or maybe there is a better way to do it.










share|improve this question









New contributor




Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.















  • 1





    Please elaborate this "I want to be able to increment the values based on the next value in the array to get this result:"

    – Syed Mehtab Hassan
    Mar 20 at 10:51











  • I want to add the numbers in the array that are next to each other together to make the next number in the array

    – Team Cafe
    Mar 20 at 10:52






  • 1





    @JollyJoker Thomas simulate .reduce method, why not use .reduce directly ?

    – R3tep
    Mar 20 at 12:26






  • 1





    @Thomas Look my answer, you can use an array as accumulator.

    – R3tep
    Mar 20 at 12:52






  • 1





    Never use forEach if you want to produce a result.

    – Bergi
    Mar 20 at 13:55













18












18








18


1






I have an array of arrays which looks like this:



changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];


I want to get the next value in the array by adding the last value



values = [ [1, 2, 3, 2], [1, 0, -1], [1, 2] ];


so far I have tried to use a forEach:



changes.forEach(change => 
let i = changes.indexOf(change);
let newValue = change[i] + change[i + 1]
);


I think I am on the right lines but I cannot get this approach to work, or maybe there is a better way to do it.










share|improve this question









New contributor




Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












I have an array of arrays which looks like this:



changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];


I want to get the next value in the array by adding the last value



values = [ [1, 2, 3, 2], [1, 0, -1], [1, 2] ];


so far I have tried to use a forEach:



changes.forEach(change => 
let i = changes.indexOf(change);
let newValue = change[i] + change[i + 1]
);


I think I am on the right lines but I cannot get this approach to work, or maybe there is a better way to do it.







javascript arrays ecmascript-6 foreach






share|improve this question









New contributor




Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|improve this question









New contributor




Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this question




share|improve this question








edited Mar 20 at 14:51









Solomon Ucko

7752822




7752822






New contributor




Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked Mar 20 at 10:47









Team CafeTeam Cafe

1065




1065




New contributor




Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





New contributor





Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Team Cafe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







  • 1





    Please elaborate this "I want to be able to increment the values based on the next value in the array to get this result:"

    – Syed Mehtab Hassan
    Mar 20 at 10:51











  • I want to add the numbers in the array that are next to each other together to make the next number in the array

    – Team Cafe
    Mar 20 at 10:52






  • 1





    @JollyJoker Thomas simulate .reduce method, why not use .reduce directly ?

    – R3tep
    Mar 20 at 12:26






  • 1





    @Thomas Look my answer, you can use an array as accumulator.

    – R3tep
    Mar 20 at 12:52






  • 1





    Never use forEach if you want to produce a result.

    – Bergi
    Mar 20 at 13:55












  • 1





    Please elaborate this "I want to be able to increment the values based on the next value in the array to get this result:"

    – Syed Mehtab Hassan
    Mar 20 at 10:51











  • I want to add the numbers in the array that are next to each other together to make the next number in the array

    – Team Cafe
    Mar 20 at 10:52






  • 1





    @JollyJoker Thomas simulate .reduce method, why not use .reduce directly ?

    – R3tep
    Mar 20 at 12:26






  • 1





    @Thomas Look my answer, you can use an array as accumulator.

    – R3tep
    Mar 20 at 12:52






  • 1





    Never use forEach if you want to produce a result.

    – Bergi
    Mar 20 at 13:55







1




1





Please elaborate this "I want to be able to increment the values based on the next value in the array to get this result:"

– Syed Mehtab Hassan
Mar 20 at 10:51





Please elaborate this "I want to be able to increment the values based on the next value in the array to get this result:"

– Syed Mehtab Hassan
Mar 20 at 10:51













I want to add the numbers in the array that are next to each other together to make the next number in the array

– Team Cafe
Mar 20 at 10:52





I want to add the numbers in the array that are next to each other together to make the next number in the array

– Team Cafe
Mar 20 at 10:52




1




1





@JollyJoker Thomas simulate .reduce method, why not use .reduce directly ?

– R3tep
Mar 20 at 12:26





@JollyJoker Thomas simulate .reduce method, why not use .reduce directly ?

– R3tep
Mar 20 at 12:26




1




1





@Thomas Look my answer, you can use an array as accumulator.

– R3tep
Mar 20 at 12:52





@Thomas Look my answer, you can use an array as accumulator.

– R3tep
Mar 20 at 12:52




1




1





Never use forEach if you want to produce a result.

– Bergi
Mar 20 at 13:55





Never use forEach if you want to produce a result.

– Bergi
Mar 20 at 13:55












7 Answers
7






active

oldest

votes


















18














You could save a sum and add the values.






var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
result = array.map(a => a.map((s => v => s += v)(0)));

console.log(result);





By using forEach, you need to take the object reference and the previous value or zero.






var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];

array.forEach(a => a.forEach((v, i, a) => a[i] = (a[i - 1] || 0) + v));

console.log(array);








share|improve this answer


















  • 1





    That first approach looks nice, but is really inefficient.

    – T.J. Crowder
    Mar 20 at 10:58






  • 11





    but man does it look nice

    – Jeremy Thille
    Mar 20 at 10:58






  • 1





    @T.J.Crowder could you explain or point me in the right direction, why the first approach is inefficient?

    – Thomas
    Mar 20 at 11:01






  • 1





    @Thomas - Look at all the functions it's creating and executing. Your solution is great -- as concise (way more so than mine) and still efficient.

    – T.J. Crowder
    Mar 20 at 11:01







  • 2





    really, for three items in the outer array? if you really want to speed up the execution, you never use some array methods, instead use nested for loops and create new arrays.

    – Nina Scholz
    Mar 20 at 11:05



















12














A version with map.






const changes = [
[1, 1, 1, -1],
[1, -1, -1],
[1, 1]
];

const values = changes.map(array =>
let acc = 0;
return array.map(v => acc += v);
);

console.log(values);

.as-console-wrappertop:0;max-height:100%!important





And this doesn't change the source Array.






share|improve this answer

























  • Note that the array of arrays structure is just a needless complication. The question is actually about the cumulative sum of an array. I'd split out the outer mapping function into something called cumulativeSum

    – JollyJoker
    Mar 20 at 12:25


















3

















const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]
let values = []
changes.forEach(arr =>
let accu = 0
let nestedArr = []
arr.forEach(n =>
accu += n
nestedArr.push(accu)
)
values.push(nestedArr)
)
console.log(values)








share|improve this answer






























    3














    You may use map function of Array




    const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]; 
    const result = changes.map((v) => v.slice(0).map((t, i, arr) => i === 0 ? t : (arr[i] += arr[i - 1])))
    console.log(changes);
    console.log(result);





    Update



    Use slice to clone array. This will prevent changes to the original array.






    share|improve this answer










    New contributor




    Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.















    • 2





      This modifies the source array, which is probably not a good idea.

      – T.J. Crowder
      Mar 20 at 10:56











    • Yes. And slice will help to prevent that. Thanks for the tip

      – Alexander
      Mar 20 at 11:02


















    3














    New ESNext features of generators are nice for this.



    Here I've created a simple sumpUp generator that you can re-use.






    function* sumUp(a) 
    let sum = 0;
    for (const v of a) yield sum += v;


    const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];
    const values = changes.map(a => [...sumUp(a)]);

    console.log(values);








    share|improve this answer
































      2














      Here is an easier to read way that iterates over the outer list of arrays. A copy of the inner array is made to keep the initial values (like [1, 1, 1, -1]). It then iterates over each value in the copied array and adds it to each index after it in the original array.






      var changes = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];
      changes.forEach(subArray =>
      var subArrayCopy = subArray.slice(); // Create a copy of the current sub array (i.e. subArrayCopy = [1, 1, 1, -1];)
      subArrayCopy.forEach((val, index) => // Iterate through each value in the copy
      for (var i = subArray.length - 1; i > index; i--) // For each element from the end to the current index
      subArray[i] += val; // Add the copy's current index value to the original array

      );
      )
      console.log(changes);








      share|improve this answer






























        1














        Another way,



        You can use .map to return your new array with the desired results. By using .reduce with an array as an accumulator, you can generate the subarray.






        var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
        result = array.map(a => a.reduce((ac, v, i) => , []));

        console.log(result);

        // shorter
        result = array.map(a => a.reduce((ac, v, i) => [...ac, (ac[i-1] || 0) + v], []));
        console.log(result);








        share|improve this answer
























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          7 Answers
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          7 Answers
          7






          active

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          oldest

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          active

          oldest

          votes









          18














          You could save a sum and add the values.






          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
          result = array.map(a => a.map((s => v => s += v)(0)));

          console.log(result);





          By using forEach, you need to take the object reference and the previous value or zero.






          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];

          array.forEach(a => a.forEach((v, i, a) => a[i] = (a[i - 1] || 0) + v));

          console.log(array);








          share|improve this answer


















          • 1





            That first approach looks nice, but is really inefficient.

            – T.J. Crowder
            Mar 20 at 10:58






          • 11





            but man does it look nice

            – Jeremy Thille
            Mar 20 at 10:58






          • 1





            @T.J.Crowder could you explain or point me in the right direction, why the first approach is inefficient?

            – Thomas
            Mar 20 at 11:01






          • 1





            @Thomas - Look at all the functions it's creating and executing. Your solution is great -- as concise (way more so than mine) and still efficient.

            – T.J. Crowder
            Mar 20 at 11:01







          • 2





            really, for three items in the outer array? if you really want to speed up the execution, you never use some array methods, instead use nested for loops and create new arrays.

            – Nina Scholz
            Mar 20 at 11:05
















          18














          You could save a sum and add the values.






          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
          result = array.map(a => a.map((s => v => s += v)(0)));

          console.log(result);





          By using forEach, you need to take the object reference and the previous value or zero.






          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];

          array.forEach(a => a.forEach((v, i, a) => a[i] = (a[i - 1] || 0) + v));

          console.log(array);








          share|improve this answer


















          • 1





            That first approach looks nice, but is really inefficient.

            – T.J. Crowder
            Mar 20 at 10:58






          • 11





            but man does it look nice

            – Jeremy Thille
            Mar 20 at 10:58






          • 1





            @T.J.Crowder could you explain or point me in the right direction, why the first approach is inefficient?

            – Thomas
            Mar 20 at 11:01






          • 1





            @Thomas - Look at all the functions it's creating and executing. Your solution is great -- as concise (way more so than mine) and still efficient.

            – T.J. Crowder
            Mar 20 at 11:01







          • 2





            really, for three items in the outer array? if you really want to speed up the execution, you never use some array methods, instead use nested for loops and create new arrays.

            – Nina Scholz
            Mar 20 at 11:05














          18












          18








          18







          You could save a sum and add the values.






          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
          result = array.map(a => a.map((s => v => s += v)(0)));

          console.log(result);





          By using forEach, you need to take the object reference and the previous value or zero.






          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];

          array.forEach(a => a.forEach((v, i, a) => a[i] = (a[i - 1] || 0) + v));

          console.log(array);








          share|improve this answer













          You could save a sum and add the values.






          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
          result = array.map(a => a.map((s => v => s += v)(0)));

          console.log(result);





          By using forEach, you need to take the object reference and the previous value or zero.






          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];

          array.forEach(a => a.forEach((v, i, a) => a[i] = (a[i - 1] || 0) + v));

          console.log(array);








          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
          result = array.map(a => a.map((s => v => s += v)(0)));

          console.log(result);





          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
          result = array.map(a => a.map((s => v => s += v)(0)));

          console.log(result);





          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];

          array.forEach(a => a.forEach((v, i, a) => a[i] = (a[i - 1] || 0) + v));

          console.log(array);





          var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];

          array.forEach(a => a.forEach((v, i, a) => a[i] = (a[i - 1] || 0) + v));

          console.log(array);






          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Mar 20 at 10:54









          Nina ScholzNina Scholz

          193k15107178




          193k15107178







          • 1





            That first approach looks nice, but is really inefficient.

            – T.J. Crowder
            Mar 20 at 10:58






          • 11





            but man does it look nice

            – Jeremy Thille
            Mar 20 at 10:58






          • 1





            @T.J.Crowder could you explain or point me in the right direction, why the first approach is inefficient?

            – Thomas
            Mar 20 at 11:01






          • 1





            @Thomas - Look at all the functions it's creating and executing. Your solution is great -- as concise (way more so than mine) and still efficient.

            – T.J. Crowder
            Mar 20 at 11:01







          • 2





            really, for three items in the outer array? if you really want to speed up the execution, you never use some array methods, instead use nested for loops and create new arrays.

            – Nina Scholz
            Mar 20 at 11:05













          • 1





            That first approach looks nice, but is really inefficient.

            – T.J. Crowder
            Mar 20 at 10:58






          • 11





            but man does it look nice

            – Jeremy Thille
            Mar 20 at 10:58






          • 1





            @T.J.Crowder could you explain or point me in the right direction, why the first approach is inefficient?

            – Thomas
            Mar 20 at 11:01






          • 1





            @Thomas - Look at all the functions it's creating and executing. Your solution is great -- as concise (way more so than mine) and still efficient.

            – T.J. Crowder
            Mar 20 at 11:01







          • 2





            really, for three items in the outer array? if you really want to speed up the execution, you never use some array methods, instead use nested for loops and create new arrays.

            – Nina Scholz
            Mar 20 at 11:05








          1




          1





          That first approach looks nice, but is really inefficient.

          – T.J. Crowder
          Mar 20 at 10:58





          That first approach looks nice, but is really inefficient.

          – T.J. Crowder
          Mar 20 at 10:58




          11




          11





          but man does it look nice

          – Jeremy Thille
          Mar 20 at 10:58





          but man does it look nice

          – Jeremy Thille
          Mar 20 at 10:58




          1




          1





          @T.J.Crowder could you explain or point me in the right direction, why the first approach is inefficient?

          – Thomas
          Mar 20 at 11:01





          @T.J.Crowder could you explain or point me in the right direction, why the first approach is inefficient?

          – Thomas
          Mar 20 at 11:01




          1




          1





          @Thomas - Look at all the functions it's creating and executing. Your solution is great -- as concise (way more so than mine) and still efficient.

          – T.J. Crowder
          Mar 20 at 11:01






          @Thomas - Look at all the functions it's creating and executing. Your solution is great -- as concise (way more so than mine) and still efficient.

          – T.J. Crowder
          Mar 20 at 11:01





          2




          2





          really, for three items in the outer array? if you really want to speed up the execution, you never use some array methods, instead use nested for loops and create new arrays.

          – Nina Scholz
          Mar 20 at 11:05






          really, for three items in the outer array? if you really want to speed up the execution, you never use some array methods, instead use nested for loops and create new arrays.

          – Nina Scholz
          Mar 20 at 11:05














          12














          A version with map.






          const changes = [
          [1, 1, 1, -1],
          [1, -1, -1],
          [1, 1]
          ];

          const values = changes.map(array =>
          let acc = 0;
          return array.map(v => acc += v);
          );

          console.log(values);

          .as-console-wrappertop:0;max-height:100%!important





          And this doesn't change the source Array.






          share|improve this answer

























          • Note that the array of arrays structure is just a needless complication. The question is actually about the cumulative sum of an array. I'd split out the outer mapping function into something called cumulativeSum

            – JollyJoker
            Mar 20 at 12:25















          12














          A version with map.






          const changes = [
          [1, 1, 1, -1],
          [1, -1, -1],
          [1, 1]
          ];

          const values = changes.map(array =>
          let acc = 0;
          return array.map(v => acc += v);
          );

          console.log(values);

          .as-console-wrappertop:0;max-height:100%!important





          And this doesn't change the source Array.






          share|improve this answer

























          • Note that the array of arrays structure is just a needless complication. The question is actually about the cumulative sum of an array. I'd split out the outer mapping function into something called cumulativeSum

            – JollyJoker
            Mar 20 at 12:25













          12












          12








          12







          A version with map.






          const changes = [
          [1, 1, 1, -1],
          [1, -1, -1],
          [1, 1]
          ];

          const values = changes.map(array =>
          let acc = 0;
          return array.map(v => acc += v);
          );

          console.log(values);

          .as-console-wrappertop:0;max-height:100%!important





          And this doesn't change the source Array.






          share|improve this answer















          A version with map.






          const changes = [
          [1, 1, 1, -1],
          [1, -1, -1],
          [1, 1]
          ];

          const values = changes.map(array =>
          let acc = 0;
          return array.map(v => acc += v);
          );

          console.log(values);

          .as-console-wrappertop:0;max-height:100%!important





          And this doesn't change the source Array.






          const changes = [
          [1, 1, 1, -1],
          [1, -1, -1],
          [1, 1]
          ];

          const values = changes.map(array =>
          let acc = 0;
          return array.map(v => acc += v);
          );

          console.log(values);

          .as-console-wrappertop:0;max-height:100%!important





          const changes = [
          [1, 1, 1, -1],
          [1, -1, -1],
          [1, 1]
          ];

          const values = changes.map(array =>
          let acc = 0;
          return array.map(v => acc += v);
          );

          console.log(values);

          .as-console-wrappertop:0;max-height:100%!important






          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Mar 20 at 11:01









          T.J. Crowder

          696k12312401334




          696k12312401334










          answered Mar 20 at 10:59









          ThomasThomas

          5,1411510




          5,1411510












          • Note that the array of arrays structure is just a needless complication. The question is actually about the cumulative sum of an array. I'd split out the outer mapping function into something called cumulativeSum

            – JollyJoker
            Mar 20 at 12:25

















          • Note that the array of arrays structure is just a needless complication. The question is actually about the cumulative sum of an array. I'd split out the outer mapping function into something called cumulativeSum

            – JollyJoker
            Mar 20 at 12:25
















          Note that the array of arrays structure is just a needless complication. The question is actually about the cumulative sum of an array. I'd split out the outer mapping function into something called cumulativeSum

          – JollyJoker
          Mar 20 at 12:25





          Note that the array of arrays structure is just a needless complication. The question is actually about the cumulative sum of an array. I'd split out the outer mapping function into something called cumulativeSum

          – JollyJoker
          Mar 20 at 12:25











          3

















          const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]
          let values = []
          changes.forEach(arr =>
          let accu = 0
          let nestedArr = []
          arr.forEach(n =>
          accu += n
          nestedArr.push(accu)
          )
          values.push(nestedArr)
          )
          console.log(values)








          share|improve this answer



























            3

















            const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]
            let values = []
            changes.forEach(arr =>
            let accu = 0
            let nestedArr = []
            arr.forEach(n =>
            accu += n
            nestedArr.push(accu)
            )
            values.push(nestedArr)
            )
            console.log(values)








            share|improve this answer

























              3












              3








              3










              const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]
              let values = []
              changes.forEach(arr =>
              let accu = 0
              let nestedArr = []
              arr.forEach(n =>
              accu += n
              nestedArr.push(accu)
              )
              values.push(nestedArr)
              )
              console.log(values)








              share|improve this answer
















              const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]
              let values = []
              changes.forEach(arr =>
              let accu = 0
              let nestedArr = []
              arr.forEach(n =>
              accu += n
              nestedArr.push(accu)
              )
              values.push(nestedArr)
              )
              console.log(values)








              const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]
              let values = []
              changes.forEach(arr =>
              let accu = 0
              let nestedArr = []
              arr.forEach(n =>
              accu += n
              nestedArr.push(accu)
              )
              values.push(nestedArr)
              )
              console.log(values)





              const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]
              let values = []
              changes.forEach(arr =>
              let accu = 0
              let nestedArr = []
              arr.forEach(n =>
              accu += n
              nestedArr.push(accu)
              )
              values.push(nestedArr)
              )
              console.log(values)






              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Mar 20 at 10:52









              holydragonholydragon

              2,69021230




              2,69021230





















                  3














                  You may use map function of Array




                  const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]; 
                  const result = changes.map((v) => v.slice(0).map((t, i, arr) => i === 0 ? t : (arr[i] += arr[i - 1])))
                  console.log(changes);
                  console.log(result);





                  Update



                  Use slice to clone array. This will prevent changes to the original array.






                  share|improve this answer










                  New contributor




                  Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.















                  • 2





                    This modifies the source array, which is probably not a good idea.

                    – T.J. Crowder
                    Mar 20 at 10:56











                  • Yes. And slice will help to prevent that. Thanks for the tip

                    – Alexander
                    Mar 20 at 11:02















                  3














                  You may use map function of Array




                  const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]; 
                  const result = changes.map((v) => v.slice(0).map((t, i, arr) => i === 0 ? t : (arr[i] += arr[i - 1])))
                  console.log(changes);
                  console.log(result);





                  Update



                  Use slice to clone array. This will prevent changes to the original array.






                  share|improve this answer










                  New contributor




                  Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.















                  • 2





                    This modifies the source array, which is probably not a good idea.

                    – T.J. Crowder
                    Mar 20 at 10:56











                  • Yes. And slice will help to prevent that. Thanks for the tip

                    – Alexander
                    Mar 20 at 11:02













                  3












                  3








                  3







                  You may use map function of Array




                  const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]; 
                  const result = changes.map((v) => v.slice(0).map((t, i, arr) => i === 0 ? t : (arr[i] += arr[i - 1])))
                  console.log(changes);
                  console.log(result);





                  Update



                  Use slice to clone array. This will prevent changes to the original array.






                  share|improve this answer










                  New contributor




                  Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.










                  You may use map function of Array




                  const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]; 
                  const result = changes.map((v) => v.slice(0).map((t, i, arr) => i === 0 ? t : (arr[i] += arr[i - 1])))
                  console.log(changes);
                  console.log(result);





                  Update



                  Use slice to clone array. This will prevent changes to the original array.






                  const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]; 
                  const result = changes.map((v) => v.slice(0).map((t, i, arr) => i === 0 ? t : (arr[i] += arr[i - 1])))
                  console.log(changes);
                  console.log(result);





                  const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ]; 
                  const result = changes.map((v) => v.slice(0).map((t, i, arr) => i === 0 ? t : (arr[i] += arr[i - 1])))
                  console.log(changes);
                  console.log(result);






                  share|improve this answer










                  New contributor




                  Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.









                  share|improve this answer



                  share|improve this answer








                  edited Mar 20 at 11:01





















                  New contributor




                  Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.









                  answered Mar 20 at 10:51









                  AlexanderAlexander

                  806112




                  806112




                  New contributor




                  Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.





                  New contributor





                  Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.






                  Alexander is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.







                  • 2





                    This modifies the source array, which is probably not a good idea.

                    – T.J. Crowder
                    Mar 20 at 10:56











                  • Yes. And slice will help to prevent that. Thanks for the tip

                    – Alexander
                    Mar 20 at 11:02












                  • 2





                    This modifies the source array, which is probably not a good idea.

                    – T.J. Crowder
                    Mar 20 at 10:56











                  • Yes. And slice will help to prevent that. Thanks for the tip

                    – Alexander
                    Mar 20 at 11:02







                  2




                  2





                  This modifies the source array, which is probably not a good idea.

                  – T.J. Crowder
                  Mar 20 at 10:56





                  This modifies the source array, which is probably not a good idea.

                  – T.J. Crowder
                  Mar 20 at 10:56













                  Yes. And slice will help to prevent that. Thanks for the tip

                  – Alexander
                  Mar 20 at 11:02





                  Yes. And slice will help to prevent that. Thanks for the tip

                  – Alexander
                  Mar 20 at 11:02











                  3














                  New ESNext features of generators are nice for this.



                  Here I've created a simple sumpUp generator that you can re-use.






                  function* sumUp(a) 
                  let sum = 0;
                  for (const v of a) yield sum += v;


                  const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];
                  const values = changes.map(a => [...sumUp(a)]);

                  console.log(values);








                  share|improve this answer





























                    3














                    New ESNext features of generators are nice for this.



                    Here I've created a simple sumpUp generator that you can re-use.






                    function* sumUp(a) 
                    let sum = 0;
                    for (const v of a) yield sum += v;


                    const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];
                    const values = changes.map(a => [...sumUp(a)]);

                    console.log(values);








                    share|improve this answer



























                      3












                      3








                      3







                      New ESNext features of generators are nice for this.



                      Here I've created a simple sumpUp generator that you can re-use.






                      function* sumUp(a) 
                      let sum = 0;
                      for (const v of a) yield sum += v;


                      const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];
                      const values = changes.map(a => [...sumUp(a)]);

                      console.log(values);








                      share|improve this answer















                      New ESNext features of generators are nice for this.



                      Here I've created a simple sumpUp generator that you can re-use.






                      function* sumUp(a) 
                      let sum = 0;
                      for (const v of a) yield sum += v;


                      const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];
                      const values = changes.map(a => [...sumUp(a)]);

                      console.log(values);








                      function* sumUp(a) 
                      let sum = 0;
                      for (const v of a) yield sum += v;


                      const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];
                      const values = changes.map(a => [...sumUp(a)]);

                      console.log(values);





                      function* sumUp(a) 
                      let sum = 0;
                      for (const v of a) yield sum += v;


                      const changes = [ [1, 1, 1, -1], [1, -1, -1], [1, 1] ];
                      const values = changes.map(a => [...sumUp(a)]);

                      console.log(values);






                      share|improve this answer














                      share|improve this answer



                      share|improve this answer








                      edited Mar 20 at 11:18

























                      answered Mar 20 at 11:13









                      KeithKeith

                      9,0301821




                      9,0301821





















                          2














                          Here is an easier to read way that iterates over the outer list of arrays. A copy of the inner array is made to keep the initial values (like [1, 1, 1, -1]). It then iterates over each value in the copied array and adds it to each index after it in the original array.






                          var changes = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];
                          changes.forEach(subArray =>
                          var subArrayCopy = subArray.slice(); // Create a copy of the current sub array (i.e. subArrayCopy = [1, 1, 1, -1];)
                          subArrayCopy.forEach((val, index) => // Iterate through each value in the copy
                          for (var i = subArray.length - 1; i > index; i--) // For each element from the end to the current index
                          subArray[i] += val; // Add the copy's current index value to the original array

                          );
                          )
                          console.log(changes);








                          share|improve this answer



























                            2














                            Here is an easier to read way that iterates over the outer list of arrays. A copy of the inner array is made to keep the initial values (like [1, 1, 1, -1]). It then iterates over each value in the copied array and adds it to each index after it in the original array.






                            var changes = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];
                            changes.forEach(subArray =>
                            var subArrayCopy = subArray.slice(); // Create a copy of the current sub array (i.e. subArrayCopy = [1, 1, 1, -1];)
                            subArrayCopy.forEach((val, index) => // Iterate through each value in the copy
                            for (var i = subArray.length - 1; i > index; i--) // For each element from the end to the current index
                            subArray[i] += val; // Add the copy's current index value to the original array

                            );
                            )
                            console.log(changes);








                            share|improve this answer

























                              2












                              2








                              2







                              Here is an easier to read way that iterates over the outer list of arrays. A copy of the inner array is made to keep the initial values (like [1, 1, 1, -1]). It then iterates over each value in the copied array and adds it to each index after it in the original array.






                              var changes = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];
                              changes.forEach(subArray =>
                              var subArrayCopy = subArray.slice(); // Create a copy of the current sub array (i.e. subArrayCopy = [1, 1, 1, -1];)
                              subArrayCopy.forEach((val, index) => // Iterate through each value in the copy
                              for (var i = subArray.length - 1; i > index; i--) // For each element from the end to the current index
                              subArray[i] += val; // Add the copy's current index value to the original array

                              );
                              )
                              console.log(changes);








                              share|improve this answer













                              Here is an easier to read way that iterates over the outer list of arrays. A copy of the inner array is made to keep the initial values (like [1, 1, 1, -1]). It then iterates over each value in the copied array and adds it to each index after it in the original array.






                              var changes = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];
                              changes.forEach(subArray =>
                              var subArrayCopy = subArray.slice(); // Create a copy of the current sub array (i.e. subArrayCopy = [1, 1, 1, -1];)
                              subArrayCopy.forEach((val, index) => // Iterate through each value in the copy
                              for (var i = subArray.length - 1; i > index; i--) // For each element from the end to the current index
                              subArray[i] += val; // Add the copy's current index value to the original array

                              );
                              )
                              console.log(changes);








                              var changes = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];
                              changes.forEach(subArray =>
                              var subArrayCopy = subArray.slice(); // Create a copy of the current sub array (i.e. subArrayCopy = [1, 1, 1, -1];)
                              subArrayCopy.forEach((val, index) => // Iterate through each value in the copy
                              for (var i = subArray.length - 1; i > index; i--) // For each element from the end to the current index
                              subArray[i] += val; // Add the copy's current index value to the original array

                              );
                              )
                              console.log(changes);





                              var changes = [[1, 1, 1, -1], [1, -1, -1], [1, 1]];
                              changes.forEach(subArray =>
                              var subArrayCopy = subArray.slice(); // Create a copy of the current sub array (i.e. subArrayCopy = [1, 1, 1, -1];)
                              subArrayCopy.forEach((val, index) => // Iterate through each value in the copy
                              for (var i = subArray.length - 1; i > index; i--) // For each element from the end to the current index
                              subArray[i] += val; // Add the copy's current index value to the original array

                              );
                              )
                              console.log(changes);






                              share|improve this answer












                              share|improve this answer



                              share|improve this answer










                              answered Mar 20 at 13:06









                              Nick GNick G

                              1,019614




                              1,019614





















                                  1














                                  Another way,



                                  You can use .map to return your new array with the desired results. By using .reduce with an array as an accumulator, you can generate the subarray.






                                  var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
                                  result = array.map(a => a.reduce((ac, v, i) => , []));

                                  console.log(result);

                                  // shorter
                                  result = array.map(a => a.reduce((ac, v, i) => [...ac, (ac[i-1] || 0) + v], []));
                                  console.log(result);








                                  share|improve this answer





























                                    1














                                    Another way,



                                    You can use .map to return your new array with the desired results. By using .reduce with an array as an accumulator, you can generate the subarray.






                                    var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
                                    result = array.map(a => a.reduce((ac, v, i) => , []));

                                    console.log(result);

                                    // shorter
                                    result = array.map(a => a.reduce((ac, v, i) => [...ac, (ac[i-1] || 0) + v], []));
                                    console.log(result);








                                    share|improve this answer



























                                      1












                                      1








                                      1







                                      Another way,



                                      You can use .map to return your new array with the desired results. By using .reduce with an array as an accumulator, you can generate the subarray.






                                      var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
                                      result = array.map(a => a.reduce((ac, v, i) => , []));

                                      console.log(result);

                                      // shorter
                                      result = array.map(a => a.reduce((ac, v, i) => [...ac, (ac[i-1] || 0) + v], []));
                                      console.log(result);








                                      share|improve this answer















                                      Another way,



                                      You can use .map to return your new array with the desired results. By using .reduce with an array as an accumulator, you can generate the subarray.






                                      var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
                                      result = array.map(a => a.reduce((ac, v, i) => , []));

                                      console.log(result);

                                      // shorter
                                      result = array.map(a => a.reduce((ac, v, i) => [...ac, (ac[i-1] || 0) + v], []));
                                      console.log(result);








                                      var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
                                      result = array.map(a => a.reduce((ac, v, i) => , []));

                                      console.log(result);

                                      // shorter
                                      result = array.map(a => a.reduce((ac, v, i) => [...ac, (ac[i-1] || 0) + v], []));
                                      console.log(result);





                                      var array = [[1, 1, 1, -1], [1, -1, -1], [1, 1]],
                                      result = array.map(a => a.reduce((ac, v, i) => , []));

                                      console.log(result);

                                      // shorter
                                      result = array.map(a => a.reduce((ac, v, i) => [...ac, (ac[i-1] || 0) + v], []));
                                      console.log(result);






                                      share|improve this answer














                                      share|improve this answer



                                      share|improve this answer








                                      edited Mar 20 at 14:37

























                                      answered Mar 20 at 12:12









                                      R3tepR3tep

                                      8,00982962




                                      8,00982962




















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