Terse Method to Swap Lowest for Highest?
$begingroup$
I have built a solution to swap the lowest values with the highest values in a list.
With
SeedRandom[987]
test = RandomSample@*Join @@ Range @@@ {{6, 10}, {56, 60}, {1, 5}, {-5, -1}}
{-1, 2, 7, 8, 60, 57, 58, 10, 9, 4, -5, -3, 3, 59, 1, 5, -4, 6, -2, 56}
Then
swapPositions =
PermutationReplace[
Ordering@Ordering@test,
With[{len = Length@test},
Cycles@
Transpose@{Range @@ {1, Floor[len/2]}, Reverse@*Range @@ {Ceiling[len/2] + 1, len}}
]
];
Sort[test][[swapPositions]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
The largest half of the numbers have had their positions swapped with lowest half of the numbers.
However, it feels too verbose and I think Sort might be expensive in this case. Is there a built-in function or more terse method to achieve this. Of course with no loss in speed. The actual case is for list of length 100000 and more.
list-manipulation performance-tuning sorting permutation
$endgroup$
add a comment |
$begingroup$
I have built a solution to swap the lowest values with the highest values in a list.
With
SeedRandom[987]
test = RandomSample@*Join @@ Range @@@ {{6, 10}, {56, 60}, {1, 5}, {-5, -1}}
{-1, 2, 7, 8, 60, 57, 58, 10, 9, 4, -5, -3, 3, 59, 1, 5, -4, 6, -2, 56}
Then
swapPositions =
PermutationReplace[
Ordering@Ordering@test,
With[{len = Length@test},
Cycles@
Transpose@{Range @@ {1, Floor[len/2]}, Reverse@*Range @@ {Ceiling[len/2] + 1, len}}
]
];
Sort[test][[swapPositions]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
The largest half of the numbers have had their positions swapped with lowest half of the numbers.
However, it feels too verbose and I think Sort might be expensive in this case. Is there a built-in function or more terse method to achieve this. Of course with no loss in speed. The actual case is for list of length 100000 and more.
list-manipulation performance-tuning sorting permutation
$endgroup$
add a comment |
$begingroup$
I have built a solution to swap the lowest values with the highest values in a list.
With
SeedRandom[987]
test = RandomSample@*Join @@ Range @@@ {{6, 10}, {56, 60}, {1, 5}, {-5, -1}}
{-1, 2, 7, 8, 60, 57, 58, 10, 9, 4, -5, -3, 3, 59, 1, 5, -4, 6, -2, 56}
Then
swapPositions =
PermutationReplace[
Ordering@Ordering@test,
With[{len = Length@test},
Cycles@
Transpose@{Range @@ {1, Floor[len/2]}, Reverse@*Range @@ {Ceiling[len/2] + 1, len}}
]
];
Sort[test][[swapPositions]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
The largest half of the numbers have had their positions swapped with lowest half of the numbers.
However, it feels too verbose and I think Sort might be expensive in this case. Is there a built-in function or more terse method to achieve this. Of course with no loss in speed. The actual case is for list of length 100000 and more.
list-manipulation performance-tuning sorting permutation
$endgroup$
I have built a solution to swap the lowest values with the highest values in a list.
With
SeedRandom[987]
test = RandomSample@*Join @@ Range @@@ {{6, 10}, {56, 60}, {1, 5}, {-5, -1}}
{-1, 2, 7, 8, 60, 57, 58, 10, 9, 4, -5, -3, 3, 59, 1, 5, -4, 6, -2, 56}
Then
swapPositions =
PermutationReplace[
Ordering@Ordering@test,
With[{len = Length@test},
Cycles@
Transpose@{Range @@ {1, Floor[len/2]}, Reverse@*Range @@ {Ceiling[len/2] + 1, len}}
]
];
Sort[test][[swapPositions]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
The largest half of the numbers have had their positions swapped with lowest half of the numbers.
However, it feels too verbose and I think Sort might be expensive in this case. Is there a built-in function or more terse method to achieve this. Of course with no loss in speed. The actual case is for list of length 100000 and more.
list-manipulation performance-tuning sorting permutation
list-manipulation performance-tuning sorting permutation
edited yesterday
J. M. is slightly pensive♦
98.4k10307466
98.4k10307466
asked yesterday
EdmundEdmund
26.7k330103
26.7k330103
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
How about:
Module[{tmp = test},
With[{ord=Ordering[tmp]},
tmp[[ord]] = Reverse @ tmp[[ord]]];
tmp
]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
$endgroup$
1
$begingroup$
That is so obvious I want to cry. Thanks (+1).
$endgroup$
– Edmund
yesterday
add a comment |
$begingroup$
This is equivalent to Carl's procedure, except that it uses one less scratch list:
With[{ord = Ordering[test]},
test[[PermutationProduct[Reverse[ord], InversePermutation[ord]]]]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
Recall that list[[perm]] = list is equivalent to list = list[[InversePermutation[perm]]], where perm is a permutation list. (The situation is equivalent to list.pmat being the same as Transpose[pmat].list if pmat is a permutation matrix.) You can then use PermutationProduct to compose successive permutations.
(This was supposed to be a comment, but it got too long.)
$endgroup$
$begingroup$
This solution doesn't copy the list so may be faster than Carl's. (+1).
$endgroup$
– Edmund
yesterday
$begingroup$
FWIW, I consistently get {56, -2, 6, -4, 5, 1, 59, 3, -3, -5, 4, 9, 10, 58, 57, 60, 8, 7, 2, -1} from this.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, what version number of Mathematica is giving that result?
$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
11.3.0.0 (5944644, 2018030701) Win 10. I did a trace, which might have had the needed info but I didn't catch it. Started w/ fresh kernel, & repeated, w/ same result. Baffled.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, can you try withWith[{ord = Ordering[test]}, test[[PermutationProduct[InversePermutation[ord], Reverse[ord]]]]]?
$endgroup$
– J. M. is slightly pensive♦
yesterday
|
show 2 more comments
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
How about:
Module[{tmp = test},
With[{ord=Ordering[tmp]},
tmp[[ord]] = Reverse @ tmp[[ord]]];
tmp
]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
$endgroup$
1
$begingroup$
That is so obvious I want to cry. Thanks (+1).
$endgroup$
– Edmund
yesterday
add a comment |
$begingroup$
How about:
Module[{tmp = test},
With[{ord=Ordering[tmp]},
tmp[[ord]] = Reverse @ tmp[[ord]]];
tmp
]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
$endgroup$
1
$begingroup$
That is so obvious I want to cry. Thanks (+1).
$endgroup$
– Edmund
yesterday
add a comment |
$begingroup$
How about:
Module[{tmp = test},
With[{ord=Ordering[tmp]},
tmp[[ord]] = Reverse @ tmp[[ord]]];
tmp
]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
$endgroup$
How about:
Module[{tmp = test},
With[{ord=Ordering[tmp]},
tmp[[ord]] = Reverse @ tmp[[ord]]];
tmp
]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
answered yesterday
Carl WollCarl Woll
71.4k394186
71.4k394186
1
$begingroup$
That is so obvious I want to cry. Thanks (+1).
$endgroup$
– Edmund
yesterday
add a comment |
1
$begingroup$
That is so obvious I want to cry. Thanks (+1).
$endgroup$
– Edmund
yesterday
1
1
$begingroup$
That is so obvious I want to cry. Thanks (+1).
$endgroup$
– Edmund
yesterday
$begingroup$
That is so obvious I want to cry. Thanks (+1).
$endgroup$
– Edmund
yesterday
add a comment |
$begingroup$
This is equivalent to Carl's procedure, except that it uses one less scratch list:
With[{ord = Ordering[test]},
test[[PermutationProduct[Reverse[ord], InversePermutation[ord]]]]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
Recall that list[[perm]] = list is equivalent to list = list[[InversePermutation[perm]]], where perm is a permutation list. (The situation is equivalent to list.pmat being the same as Transpose[pmat].list if pmat is a permutation matrix.) You can then use PermutationProduct to compose successive permutations.
(This was supposed to be a comment, but it got too long.)
$endgroup$
$begingroup$
This solution doesn't copy the list so may be faster than Carl's. (+1).
$endgroup$
– Edmund
yesterday
$begingroup$
FWIW, I consistently get {56, -2, 6, -4, 5, 1, 59, 3, -3, -5, 4, 9, 10, 58, 57, 60, 8, 7, 2, -1} from this.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, what version number of Mathematica is giving that result?
$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
11.3.0.0 (5944644, 2018030701) Win 10. I did a trace, which might have had the needed info but I didn't catch it. Started w/ fresh kernel, & repeated, w/ same result. Baffled.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, can you try withWith[{ord = Ordering[test]}, test[[PermutationProduct[InversePermutation[ord], Reverse[ord]]]]]?
$endgroup$
– J. M. is slightly pensive♦
yesterday
|
show 2 more comments
$begingroup$
This is equivalent to Carl's procedure, except that it uses one less scratch list:
With[{ord = Ordering[test]},
test[[PermutationProduct[Reverse[ord], InversePermutation[ord]]]]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
Recall that list[[perm]] = list is equivalent to list = list[[InversePermutation[perm]]], where perm is a permutation list. (The situation is equivalent to list.pmat being the same as Transpose[pmat].list if pmat is a permutation matrix.) You can then use PermutationProduct to compose successive permutations.
(This was supposed to be a comment, but it got too long.)
$endgroup$
$begingroup$
This solution doesn't copy the list so may be faster than Carl's. (+1).
$endgroup$
– Edmund
yesterday
$begingroup$
FWIW, I consistently get {56, -2, 6, -4, 5, 1, 59, 3, -3, -5, 4, 9, 10, 58, 57, 60, 8, 7, 2, -1} from this.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, what version number of Mathematica is giving that result?
$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
11.3.0.0 (5944644, 2018030701) Win 10. I did a trace, which might have had the needed info but I didn't catch it. Started w/ fresh kernel, & repeated, w/ same result. Baffled.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, can you try withWith[{ord = Ordering[test]}, test[[PermutationProduct[InversePermutation[ord], Reverse[ord]]]]]?
$endgroup$
– J. M. is slightly pensive♦
yesterday
|
show 2 more comments
$begingroup$
This is equivalent to Carl's procedure, except that it uses one less scratch list:
With[{ord = Ordering[test]},
test[[PermutationProduct[Reverse[ord], InversePermutation[ord]]]]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
Recall that list[[perm]] = list is equivalent to list = list[[InversePermutation[perm]]], where perm is a permutation list. (The situation is equivalent to list.pmat being the same as Transpose[pmat].list if pmat is a permutation matrix.) You can then use PermutationProduct to compose successive permutations.
(This was supposed to be a comment, but it got too long.)
$endgroup$
This is equivalent to Carl's procedure, except that it uses one less scratch list:
With[{ord = Ordering[test]},
test[[PermutationProduct[Reverse[ord], InversePermutation[ord]]]]]
{56, 9, 4, 3, -5, -2, -3, 1, 2, 7, 60, 58, 8, -4, 10, 6, 59, 5, 57, -1}
Recall that list[[perm]] = list is equivalent to list = list[[InversePermutation[perm]]], where perm is a permutation list. (The situation is equivalent to list.pmat being the same as Transpose[pmat].list if pmat is a permutation matrix.) You can then use PermutationProduct to compose successive permutations.
(This was supposed to be a comment, but it got too long.)
edited yesterday
answered yesterday
J. M. is slightly pensive♦J. M. is slightly pensive
98.4k10307466
98.4k10307466
$begingroup$
This solution doesn't copy the list so may be faster than Carl's. (+1).
$endgroup$
– Edmund
yesterday
$begingroup$
FWIW, I consistently get {56, -2, 6, -4, 5, 1, 59, 3, -3, -5, 4, 9, 10, 58, 57, 60, 8, 7, 2, -1} from this.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, what version number of Mathematica is giving that result?
$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
11.3.0.0 (5944644, 2018030701) Win 10. I did a trace, which might have had the needed info but I didn't catch it. Started w/ fresh kernel, & repeated, w/ same result. Baffled.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, can you try withWith[{ord = Ordering[test]}, test[[PermutationProduct[InversePermutation[ord], Reverse[ord]]]]]?
$endgroup$
– J. M. is slightly pensive♦
yesterday
|
show 2 more comments
$begingroup$
This solution doesn't copy the list so may be faster than Carl's. (+1).
$endgroup$
– Edmund
yesterday
$begingroup$
FWIW, I consistently get {56, -2, 6, -4, 5, 1, 59, 3, -3, -5, 4, 9, 10, 58, 57, 60, 8, 7, 2, -1} from this.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, what version number of Mathematica is giving that result?
$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
11.3.0.0 (5944644, 2018030701) Win 10. I did a trace, which might have had the needed info but I didn't catch it. Started w/ fresh kernel, & repeated, w/ same result. Baffled.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, can you try withWith[{ord = Ordering[test]}, test[[PermutationProduct[InversePermutation[ord], Reverse[ord]]]]]?
$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
This solution doesn't copy the list so may be faster than Carl's. (+1).
$endgroup$
– Edmund
yesterday
$begingroup$
This solution doesn't copy the list so may be faster than Carl's. (+1).
$endgroup$
– Edmund
yesterday
$begingroup$
FWIW, I consistently get {56, -2, 6, -4, 5, 1, 59, 3, -3, -5, 4, 9, 10, 58, 57, 60, 8, 7, 2, -1} from this.
$endgroup$
– Rabbit
yesterday
$begingroup$
FWIW, I consistently get {56, -2, 6, -4, 5, 1, 59, 3, -3, -5, 4, 9, 10, 58, 57, 60, 8, 7, 2, -1} from this.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, what version number of Mathematica is giving that result?
$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
@Rabbit, what version number of Mathematica is giving that result?
$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
11.3.0.0 (5944644, 2018030701) Win 10. I did a trace, which might have had the needed info but I didn't catch it. Started w/ fresh kernel, & repeated, w/ same result. Baffled.
$endgroup$
– Rabbit
yesterday
$begingroup$
11.3.0.0 (5944644, 2018030701) Win 10. I did a trace, which might have had the needed info but I didn't catch it. Started w/ fresh kernel, & repeated, w/ same result. Baffled.
$endgroup$
– Rabbit
yesterday
$begingroup$
@Rabbit, can you try with
With[{ord = Ordering[test]}, test[[PermutationProduct[InversePermutation[ord], Reverse[ord]]]]]?$endgroup$
– J. M. is slightly pensive♦
yesterday
$begingroup$
@Rabbit, can you try with
With[{ord = Ordering[test]}, test[[PermutationProduct[InversePermutation[ord], Reverse[ord]]]]]?$endgroup$
– J. M. is slightly pensive♦
yesterday
|
show 2 more comments
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