Inexact numbers as keys in Association? The 2019 Stack Overflow Developer Survey Results Are In Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)Dr. StrangeNumbers or: How I Learned to Stop Worrying and Love Floating Point ArithmeticFractional Keys in AssociationsReplace and AssociationWrong Limit[…] for inexact expressionsPicking out multiple keys from an arrayUsing Case to pull Keys and Values out of a nested AssociationPattern matching Association in rulesCreating dataset from list of ragged associations with defaults for missing keyshow to count or extract Cases out of list of association that matches patternRename Keys in Nested AssociationExtracting the graph of Keys in nested Associations
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Inexact numbers as keys in Association?
The 2019 Stack Overflow Developer Survey Results Are In
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)Dr. StrangeNumbers or: How I Learned to Stop Worrying and Love Floating Point ArithmeticFractional Keys in AssociationsReplace and AssociationWrong Limit[…] for inexact expressionsPicking out multiple keys from an arrayUsing Case to pull Keys and Values out of a nested AssociationPattern matching Association in rulesCreating dataset from list of ragged associations with defaults for missing keyshow to count or extract Cases out of list of association that matches patternRename Keys in Nested AssociationExtracting the graph of Keys in nested Associations
$begingroup$
Can someone explain me how Mathematica's Associations behave with inexact numbers as keys:
<| 0.22499999999999964` -> a |> [0.22499999999999965`]
and
<| 0.22499999999999964` -> a |> [0.22499999999999961`]
both give the value a, whereas
<| 0.22499999999999964` -> a |> [0.22499999999999966`] gives Missing as an answer.
associations machine-precision
edited Apr 1 at 6:21
J. M. is away♦
98.9k10311467
asked Mar 31 at 13:38
Ali HashmiAli Hashmi
5,73931433
$endgroup$
add a comment |
$begingroup$
Can someone explain me how Mathematica's Associations behave with inexact numbers as keys:
<| 0.22499999999999964` -> a |> [0.22499999999999965`]
and
<| 0.22499999999999964` -> a |> [0.22499999999999961`]
both give the value a, whereas
<| 0.22499999999999964` -> a |> [0.22499999999999966`] gives Missing as an answer.
associations machine-precision
edited Apr 1 at 6:21
J. M. is away♦
98.9k10311467
asked Mar 31 at 13:38
Ali HashmiAli Hashmi
5,73931433
$endgroup$
2
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is away♦
Mar 31 at 13:50
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
Mar 31 at 13:51
$begingroup$
Associationis the name of the function in Mathematica, so I am not sure what was productive about the edit I just rolled back.
$endgroup$
– J. M. is away♦
Apr 1 at 6:22
add a comment |
$begingroup$
Can someone explain me how Mathematica's Associations behave with inexact numbers as keys:
<| 0.22499999999999964` -> a |> [0.22499999999999965`]
and
<| 0.22499999999999964` -> a |> [0.22499999999999961`]
both give the value a, whereas
<| 0.22499999999999964` -> a |> [0.22499999999999966`] gives Missing as an answer.
associations machine-precision
edited Apr 1 at 6:21
J. M. is away♦
98.9k10311467
asked Mar 31 at 13:38
Ali HashmiAli Hashmi
5,73931433
$endgroup$
Can someone explain me how Mathematica's Associations behave with inexact numbers as keys:
<| 0.22499999999999964` -> a |> [0.22499999999999965`]
and
<| 0.22499999999999964` -> a |> [0.22499999999999961`]
both give the value a, whereas
<| 0.22499999999999964` -> a |> [0.22499999999999966`] gives Missing as an answer.
associations machine-precision
associations machine-precision
edited Apr 1 at 6:21
J. M. is away♦
98.9k10311467
asked Mar 31 at 13:38
Ali HashmiAli Hashmi
5,73931433
edited Apr 1 at 6:21
J. M. is away♦
98.9k10311467
asked Mar 31 at 13:38
Ali HashmiAli Hashmi
5,73931433
edited Apr 1 at 6:21
J. M. is away♦
98.9k10311467
edited Apr 1 at 6:21
J. M. is away♦
98.9k10311467
edited Apr 1 at 6:21
J. M. is away♦
98.9k10311467
98.9k10311467
asked Mar 31 at 13:38
Ali HashmiAli Hashmi
5,73931433
asked Mar 31 at 13:38
Ali HashmiAli Hashmi
5,73931433
asked Mar 31 at 13:38
Ali HashmiAli Hashmi
5,73931433
5,73931433
2
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is away♦
Mar 31 at 13:50
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
Mar 31 at 13:51
$begingroup$
Associationis the name of the function in Mathematica, so I am not sure what was productive about the edit I just rolled back.
$endgroup$
– J. M. is away♦
Apr 1 at 6:22
add a comment |
2
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is away♦
Mar 31 at 13:50
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
Mar 31 at 13:51
$begingroup$
Associationis the name of the function in Mathematica, so I am not sure what was productive about the edit I just rolled back.
$endgroup$
– J. M. is away♦
Apr 1 at 6:22
2
2
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is away♦
Mar 31 at 13:50
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is away♦
Mar 31 at 13:50
4
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
Mar 31 at 13:51
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
Mar 31 at 13:51
$begingroup$
Association is the name of the function in Mathematica, so I am not sure what was productive about the edit I just rolled back.$endgroup$
– J. M. is away♦
Apr 1 at 6:22
$begingroup$
Association is the name of the function in Mathematica, so I am not sure what was productive about the edit I just rolled back.$endgroup$
– J. M. is away♦
Apr 1 at 6:22
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
Lookups with inexact numbers behave like other lookups: they use hashing. We can check that the results are consistent with what Hash does.
vals = 0.22499999999999961`, 0.22499999999999964`,
0.22499999999999965`, 0.22499999999999966`;
Hash /@ vals
(* Out[11]= 1879126079618645156, 1879126079618645156,
1879126079618645156, 5861724109654749116 *)
When hashing approximate values, there are going to be sharp boundaries (discontinuities, in effect). This is a tradeoff between having "very" close neighbors hash to the same value, and maintaining transitivity.
answered Mar 31 at 13:59
Daniel LichtblauDaniel Lichtblau
47.6k277165
$endgroup$
add a comment |
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$begingroup$
Lookups with inexact numbers behave like other lookups: they use hashing. We can check that the results are consistent with what Hash does.
vals = 0.22499999999999961`, 0.22499999999999964`,
0.22499999999999965`, 0.22499999999999966`;
Hash /@ vals
(* Out[11]= 1879126079618645156, 1879126079618645156,
1879126079618645156, 5861724109654749116 *)
When hashing approximate values, there are going to be sharp boundaries (discontinuities, in effect). This is a tradeoff between having "very" close neighbors hash to the same value, and maintaining transitivity.
answered Mar 31 at 13:59
Daniel LichtblauDaniel Lichtblau
47.6k277165
$endgroup$
add a comment |
$begingroup$
Lookups with inexact numbers behave like other lookups: they use hashing. We can check that the results are consistent with what Hash does.
vals = 0.22499999999999961`, 0.22499999999999964`,
0.22499999999999965`, 0.22499999999999966`;
Hash /@ vals
(* Out[11]= 1879126079618645156, 1879126079618645156,
1879126079618645156, 5861724109654749116 *)
When hashing approximate values, there are going to be sharp boundaries (discontinuities, in effect). This is a tradeoff between having "very" close neighbors hash to the same value, and maintaining transitivity.
answered Mar 31 at 13:59
Daniel LichtblauDaniel Lichtblau
47.6k277165
$endgroup$
add a comment |
$begingroup$
Lookups with inexact numbers behave like other lookups: they use hashing. We can check that the results are consistent with what Hash does.
vals = 0.22499999999999961`, 0.22499999999999964`,
0.22499999999999965`, 0.22499999999999966`;
Hash /@ vals
(* Out[11]= 1879126079618645156, 1879126079618645156,
1879126079618645156, 5861724109654749116 *)
When hashing approximate values, there are going to be sharp boundaries (discontinuities, in effect). This is a tradeoff between having "very" close neighbors hash to the same value, and maintaining transitivity.
answered Mar 31 at 13:59
Daniel LichtblauDaniel Lichtblau
47.6k277165
$endgroup$
Lookups with inexact numbers behave like other lookups: they use hashing. We can check that the results are consistent with what Hash does.
vals = 0.22499999999999961`, 0.22499999999999964`,
0.22499999999999965`, 0.22499999999999966`;
Hash /@ vals
(* Out[11]= 1879126079618645156, 1879126079618645156,
1879126079618645156, 5861724109654749116 *)
When hashing approximate values, there are going to be sharp boundaries (discontinuities, in effect). This is a tradeoff between having "very" close neighbors hash to the same value, and maintaining transitivity.
answered Mar 31 at 13:59
Daniel LichtblauDaniel Lichtblau
47.6k277165
answered Mar 31 at 13:59
Daniel LichtblauDaniel Lichtblau
47.6k277165
answered Mar 31 at 13:59
Daniel LichtblauDaniel Lichtblau
47.6k277165
answered Mar 31 at 13:59
Daniel LichtblauDaniel Lichtblau
47.6k277165
47.6k277165
add a comment |
add a comment |
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2
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is away♦
Mar 31 at 13:50
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
Mar 31 at 13:51
$begingroup$
Associationis the name of the function in Mathematica, so I am not sure what was productive about the edit I just rolled back.$endgroup$
– J. M. is away♦
Apr 1 at 6:22