Timeline for Thread a function over a list and with a non-atomic 2nd parameter?
Current License: CC BY-SA 3.0
19 events
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| Aug 28, 2012 at 17:57 | comment | added | alancalvitti | @kguler, ... I'm trying to emulate this function using Thread: MapIfList[f_, x_] := If[Length[x] > 0, Map[f, x], f[x]] | |
| Aug 28, 2012 at 17:56 | comment | added | alancalvitti | @kguler, that works on lists of dates but not singletons (Thread[Unevaluated@SelectInFrame[{2007, 1, 30}, m2], List, 1] --> {{}, {}, {}} ) . The purpose of this Thread construction is to selectively map on lists but also on singleton arguments | |
| Aug 28, 2012 at 2:40 | comment | added | kglr |
@alan, I am not sure if this answers the question in your comment: with m2 as above, Thread[Unevaluated@ SelectInFrame[{{2008, 2, 23}, DateList[{2009, 10, 14}][[;; 3]]}, m2], List, 1] gives {{{{2008, 2, 23}, 4, "y"}}, {{{2009, 10, 14}, 5, "z"}}}.
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| Aug 28, 2012 at 1:14 | comment | added | alancalvitti | @kguler, yes, only the 1st row or 1st column (part of the "frame") elements are changed from String to List as you show - the remaining elements can stay numbers or anything else. I describe this issue more in my own answer to the question here: mathematica.stackexchange.com/questions/9702/… | |
| Aug 27, 2012 at 21:50 | comment | added | kglr |
@alan, can you give the examples of M and Thread usage mentioned in your comment where Thread[...,{2}] works/does not work? Is M something like m2 = {{{2007, 1, 30}, 3, "x"}, {{2008, 2, 23}, 4, "y"}, {{2009, 10, 14}, 5, "z"}}?
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| Aug 27, 2012 at 20:33 | comment | added | alancalvitti | @kguler, can you extend this answer if the first column of M contains Lists, eg {2012,8,25} rather than Strings? I find that it works if the last argument to Thread is {2} to match a single such list, but doesn't match lists of lists, eg {{2012,8,25},{2012,8,27}} (assuming M contains those). | |
| Aug 27, 2012 at 1:18 | comment | added | kglr |
Thread evaluates the whole expression before threading. You need to use Unevaluated to prevent this behavior. So, Thread[Unevaluated@SelectInFrame[2, M], List, 1] gives {{2,3}} and Thread[Unevaluated@SelectInFrame[{2, 3}, M], List, 1] gives {{{2, 3}}, {{3, 4}}}.
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| Aug 26, 2012 at 18:59 | comment | added | alancalvitti | @kguler, I can't get the desired behavior with the following function: SelectInFrame[h_, data_] := Select[data, #[[1]] == h &]. Using the same M, Thread[SelectInFrame[2, M], List, 1] --> {{2}, {3}} (it should be {2,3}) and Thread[SelectInFrame[{2, 3}, M], List, 1] returns error: "Thread::tpos: Cannot thread over positions 1 through 1 in {}". ? | |
| Aug 25, 2012 at 23:18 | comment | added | kglr | alan, btw just noticed that @Leonid's answer and comment already adresses this question. | |
| Aug 25, 2012 at 23:06 | comment | added | kglr |
@alancalvitti, in effect you want to change the behavior of the attribute Listable to thread over selected arguments? I would defer to Leonid/Rojo/... on whether this is possible/advisable:)
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| Aug 25, 2012 at 22:35 | comment | added | alancalvitti | Very nice. Is there any way to make Listable work with these options? | |
| Aug 25, 2012 at 22:31 | history | edited | kglr | CC BY-SA 3.0 |
added 139 characters in body; added 4 characters in body
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| Aug 25, 2012 at 22:27 | comment | added | Mr.Wizard |
I am mistaken, it does! Thread[f[M, {a, b, c}], List, {2}] (For some reason I didn't think that worked.)
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| Aug 25, 2012 at 22:25 | comment | added | Mr.Wizard |
+1 because this is useful information and the question is not well defined, but I interpret that the solution should also handle f[M, {a, b, c}] and this, as written, does not.
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| Aug 25, 2012 at 22:22 | history | edited | kglr | CC BY-SA 3.0 |
added 79 characters in body; added 139 characters in body
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| Aug 25, 2012 at 22:22 | history | undeleted | kglr | ||
| Aug 25, 2012 at 22:14 | history | deleted | kglr | ||
| Aug 25, 2012 at 22:14 | review | Low quality posts | |||
| Aug 25, 2012 at 22:19 | |||||
| Aug 25, 2012 at 22:13 | history | answered | kglr | CC BY-SA 3.0 |