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Reduce array of object to totals by property object

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6

0

I'm looking for a smart ES6 way to reduce array of objects into totals-by-property-object.

for a sample data:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

following code:

const res = src.reduce((totals,item) => Object.keys(item).forEach(weekday => totals[weekday] += item[weekday]),)

throws an error:

Uncaught TypeError: Cannot read property 'mon' of undefined

even if reduce is initialized with mon:0, tue:0 ... instead of .

Is there a non-for-loop solution?

p.s. expected output is an object where each property is a sum of array objects by that property, e.g. mon:6, tue:3, wed:5, thu:5, fri:8, sat:0, sun:10 in my case

javascript ecmascript-6

share|improve this question

edited Mar 29 at 13:18

user11154868

asked Mar 29 at 13:13

user11154868user11154868

334

add a comment | 

6

0

I'm looking for a smart ES6 way to reduce array of objects into totals-by-property-object.

for a sample data:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

following code:

const res = src.reduce((totals,item) => Object.keys(item).forEach(weekday => totals[weekday] += item[weekday]),)

throws an error:

Uncaught TypeError: Cannot read property 'mon' of undefined

even if reduce is initialized with mon:0, tue:0 ... instead of .

Is there a non-for-loop solution?

p.s. expected output is an object where each property is a sum of array objects by that property, e.g. mon:6, tue:3, wed:5, thu:5, fri:8, sat:0, sun:10 in my case

javascript ecmascript-6

share|improve this question

edited Mar 29 at 13:18

user11154868

asked Mar 29 at 13:13

user11154868user11154868

334

add a comment | 

I'm looking for a smart ES6 way to reduce array of objects into totals-by-property-object.

for a sample data:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

following code:

const res = src.reduce((totals,item) => Object.keys(item).forEach(weekday => totals[weekday] += item[weekday]),)

throws an error:

Uncaught TypeError: Cannot read property 'mon' of undefined

even if reduce is initialized with mon:0, tue:0 ... instead of .

Is there a non-for-loop solution?

p.s. expected output is an object where each property is a sum of array objects by that property, e.g. mon:6, tue:3, wed:5, thu:5, fri:8, sat:0, sun:10 in my case

javascript ecmascript-6

share|improve this question

edited Mar 29 at 13:18

user11154868

asked Mar 29 at 13:13

user11154868user11154868

334

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals,item) => Object.keys(item).forEach(weekday => totals[weekday] += item[weekday]),)

share|improve this question

edited Mar 29 at 13:18

user11154868

asked Mar 29 at 13:13

user11154868user11154868

334

share|improve this question

edited Mar 29 at 13:18

user11154868

asked Mar 29 at 13:13

user11154868user11154868

334

asked Mar 29 at 13:13

user11154868user11154868

334

asked Mar 29 at 13:13

user11154868user11154868

334

2 Answers
2

active

oldest

votes

5

You need to return totals after you modify it:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 
 Object.keys(item).forEach(weekday => totals[weekday] = (totals[weekday] , );

console.log(res);

share|improve this answer

edited Apr 1 at 4:52

answered Mar 29 at 13:17

Ori DroriOri Drori

82.3k148998

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I can't believe it was that close. Thanks a lot.
  
  – user11154868
  Mar 29 at 13:24
  

  
  
  
  

add a comment | 

4

You need to return totals as accumulator for reduce.

If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered Mar 29 at 13:17

Nina ScholzNina Scholz

197k15110179

add a comment | 

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5

You need to return totals after you modify it:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 
 Object.keys(item).forEach(weekday => totals[weekday] = (totals[weekday] , );

console.log(res);

share|improve this answer

edited Apr 1 at 4:52

answered Mar 29 at 13:17

Ori DroriOri Drori

82.3k148998

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I can't believe it was that close. Thanks a lot.
  
  – user11154868
  Mar 29 at 13:24
  

  
  
  
  

add a comment | 

5

You need to return totals after you modify it:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 
 Object.keys(item).forEach(weekday => totals[weekday] = (totals[weekday] , );

console.log(res);

share|improve this answer

edited Apr 1 at 4:52

answered Mar 29 at 13:17

Ori DroriOri Drori

82.3k148998

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I can't believe it was that close. Thanks a lot.
  
  – user11154868
  Mar 29 at 13:24
  

  
  
  
  

add a comment | 

You need to return totals after you modify it:

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 
 Object.keys(item).forEach(weekday => totals[weekday] = (totals[weekday] , );

console.log(res);

share|improve this answer

edited Apr 1 at 4:52

answered Mar 29 at 13:17

Ori DroriOri Drori

82.3k148998

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 
 Object.keys(item).forEach(weekday => totals[weekday] = (totals[weekday] , );

console.log(res);

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 
 Object.keys(item).forEach(weekday => totals[weekday] = (totals[weekday] , );

console.log(res);

const src = [mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4, mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6];

const res = src.reduce((totals, item) => 
 Object.keys(item).forEach(weekday => totals[weekday] = (totals[weekday] , );

console.log(res);

share|improve this answer

edited Apr 1 at 4:52

answered Mar 29 at 13:17

Ori DroriOri Drori

82.3k148998

answered Mar 29 at 13:17

Ori DroriOri Drori

82.3k148998

answered Mar 29 at 13:17

Ori DroriOri Drori

82.3k148998

4

You need to return totals as accumulator for reduce.

If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered Mar 29 at 13:17

Nina ScholzNina Scholz

197k15110179

add a comment | 

4

You need to return totals as accumulator for reduce.

If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered Mar 29 at 13:17

Nina ScholzNina Scholz

197k15110179

add a comment | 

You need to return totals as accumulator for reduce.

If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered Mar 29 at 13:17

Nina ScholzNina Scholz

197k15110179

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

const
 src = [ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 , mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 ],
 res = src.reduce((totals, item) => 
 (Object.keys(item).forEach(d => totals[d] += item[d]), totals));

console.log(res);

share|improve this answer

answered Mar 29 at 13:17

Nina ScholzNina Scholz

197k15110179

answered Mar 29 at 13:17

Nina ScholzNina Scholz

197k15110179

answered Mar 29 at 13:17

Nina ScholzNina Scholz

197k15110179