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Wolfram Function Repository

Instant-use add-on functions for the Wolfram Language

Function Repository Resource:

 KeyMapIf

Source Notebook

Map a function conditionally over keys in an association

Contributed by: Seth J. Chandler

ResourceFunction["KeyMapIf"][f,test,assoc]

applies f to only those keys ki in assoc for which test[ki] gives True.

ResourceFunction["KeyMapIf"][f,test]

is the operator form of ResourceFunction["KeyMapIf"].

Details and Options

ResourceFunction["KeyMapIf"] uses the same programming constructs as the resource function MapIf.

Examples

Basic Examples (3) 

Map the function f over the keys of an Association, but only if the key is a string:

In[1]:=
ResourceFunction["KeyMapIf"][f, StringQ, Association["a" -> 4, 3 -> 5]]
Out[1]=
Image

Turn any keys that are numeric in an Association into strings, using InputForm to show that it worked:

In[2]:=
ResourceFunction["KeyMapIf"][ToString, NumericQ, Association["a" -> 4, 3 -> 5]] // InputForm
Out[514]=
Image

Use the operator form, using the resource function ShowQuotes to show that it worked:

In[515]:=
ResourceFunction["KeyMapIf"][ToString, NumericQ][ Association["a" -> 4, 3 -> 5]] // ResourceFunction["ShowQuotes"]
Out[515]=
Image

Applications (1) 

Compare the output from an EntityValue operation before KeyMapIf is used with the much nicer output after being adjusted by KeyMapIf:

In[516]:=
With[{output = EntityValue[ SampledEntityClass[ "DogBreed", {6, 9}], {EntityProperty["DogBreed", "Shedding"], "WeightMaleMean"}, "EntityPropertyAssociation"]}, Column@{Framed@Labeled[Dataset[output], "before"], Framed@Labeled[ Dataset[Query[ ResourceFunction["KeyMapIf"][CanonicalName, MatchQ[#, _Entity] &], ResourceFunction["KeyMapIf"][CanonicalName, MatchQ[#, _EntityProperty] &]][output]], "after"]}]
Out[516]=
Image

Properties and Relations (2) 

As with the resource function MapIf, KeyMapIf does not itself support level specifications. KeyMapIf can operate at deeper levels of an Association, however, through the use of Query:

In[517]:=
Query[All, ResourceFunction["KeyMapIf"][f, StringQ]][{Association["a" -> 4, "b" -> 6], Association["a" -> 5, x -> 8]}]
Out[517]=
Image

KeyMapIf can work on an Association of associations contained in a Dataset (or even more deeply):

In[518]:=
Query[ResourceFunction["KeyMapIf"][StringReverse, StringContainsQ[#, "n"] &], ResourceFunction["KeyMapIf"][f, StringQ]][ Dataset[Association["1st" -> Association["a" -> 4, 5 -> 6], "2nd" -> Association["a" -> 5, 5 -> 8]]]]
Out[518]=
Image

Publisher

Seth J. Chandler

Version History

  • 1.0.0 – 26 July 2019

Related Resources

License Information