Inexact numbers as keys in Association?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?
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 yesterday
J. M. is slightly pensive♦
98.9k10311467
asked 2 days ago
Ali HashmiAli Hashmi
5,71931432
$endgroup$
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 yesterday
J. M. is slightly pensive♦
98.9k10311467
asked 2 days ago
Ali HashmiAli Hashmi
5,71931432
$endgroup$
2
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is slightly pensive♦
2 days ago
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
2 days ago
$begingroup$
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 slightly pensive♦
yesterday
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 yesterday
J. M. is slightly pensive♦
98.9k10311467
asked 2 days ago
Ali HashmiAli Hashmi
5,71931432
$endgroup$
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 yesterday
J. M. is slightly pensive♦
98.9k10311467
asked 2 days ago
Ali HashmiAli Hashmi
5,71931432
edited yesterday
J. M. is slightly pensive♦
98.9k10311467
asked 2 days ago
Ali HashmiAli Hashmi
5,71931432
edited yesterday
J. M. is slightly pensive♦
98.9k10311467
edited yesterday
J. M. is slightly pensive♦
98.9k10311467
edited yesterday
J. M. is slightly pensive♦
98.9k10311467
98.9k10311467
asked 2 days ago
Ali HashmiAli Hashmi
5,71931432
asked 2 days ago
Ali HashmiAli Hashmi
5,71931432
asked 2 days ago
Ali HashmiAli Hashmi
5,71931432
5,71931432
2
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is slightly pensive♦
2 days ago
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
2 days ago
$begingroup$
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 slightly pensive♦
yesterday
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 slightly pensive♦
2 days ago
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
2 days ago
$begingroup$
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 slightly pensive♦
yesterday
2
2
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is slightly pensive♦
2 days ago
$begingroup$
Looks like this thing, but with associations. Why do you need to use inexact numbers as keys?
$endgroup$
– J. M. is slightly pensive♦
2 days ago
4
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
2 days ago
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
2 days ago
$begingroup$
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 slightly pensive♦
yesterday
$begingroup$
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 slightly pensive♦
yesterday
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 2 days ago
Daniel LichtblauDaniel Lichtblau
47.5k277165
$endgroup$
add a comment |
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1 Answer
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oldest
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1 Answer
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active
oldest
votes
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oldest
votes
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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 2 days ago
Daniel LichtblauDaniel Lichtblau
47.5k277165
$endgroup$
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 2 days ago
Daniel LichtblauDaniel Lichtblau
47.5k277165
$endgroup$
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 2 days ago
Daniel LichtblauDaniel Lichtblau
47.5k277165
$endgroup$
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 2 days ago
Daniel LichtblauDaniel Lichtblau
47.5k277165
answered 2 days ago
Daniel LichtblauDaniel Lichtblau
47.5k277165
answered 2 days ago
Daniel LichtblauDaniel Lichtblau
47.5k277165
answered 2 days ago
Daniel LichtblauDaniel Lichtblau
47.5k277165
47.5k277165
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 slightly pensive♦
2 days ago
4
$begingroup$
"Can someone explain me how Mathematica's Associations behave [...]?" They behave badly. Don't do that.
$endgroup$
– Henrik Schumacher
2 days ago
$begingroup$
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 slightly pensive♦
yesterday