Function Repository Resource:

MapAtKey

Apply functions to specific keys in an association

Contributed by: Bob Sandheinrich

ResourceFunction["MapAtKey"][{key₁→f₁,…},assoc]

gives an association with each f_i applied to the value of key_i in assoc.

Details and Options

Keys not included in the rules will maintain the same values in the result.

Selectively modify values in an Association:

In[1]:=

$ResourceFunction[ "MapAtKey"][{"a" -> (#^2 &), "b" -> (#/2 &)}, <|"a" -> 10, "b" -> 2, "c" -> 3|>]$

Out[1]=

All specified keys must exist in the Association:

In[2]:=

$ResourceFunction[ "MapAtKey"][{"a" -> (#^2 &), "d" -> (#/2 &)}, <|"a" -> 10, "b" -> 2, "c" -> 3|>]$

Out[2]=

Wolfram Language 11.3 (March 2018) or above