Wolfram Function Repository

Instant-use add-on functions for the Wolfram Language

Function Repository Resource:

 AssociationMapAt

Source Notebook

Similar to MapAt but with improved behavior for nested expressions involving associations

Contributed by: Paco Jain (Wolfram Research)

ResourceFunction["AssociationMapAt"][f,assoc,atSpec]

applies f to the association assoc at the position(s) specified by atSpec.

Details and Options

ResourceFunction["AssociationMapAt"] is similar in usage to MapAt but has different behavior when used with associations.
For its third argument, ResourceFunction["AssociationMapAt"] takes a list consisting of any of the following: explicit integers, Span expressions, strings, Key expressions or All.
ResourceFunction["AssociationMapAt"] will not give messages if the position specified by atSpec does not exist, or is ragged, in assoc. Contrast ResourceFunction["AssociationMapAt"][f,<|"a"→<||>,"b"→<|"x"→1|>|>,{All,"x"}] with MapAt[f,<|"a"→<||>,"b"→<|"x"→1|>|>,{All,"x"}].

Examples

Basic Examples (3) 

Apply a function to parts of a nested association:

In[1]:=
testAssoc = <|"chem1" -> <|"Density" -> 12, "Color" -> White|>, "chem2" -> <|"Color" -> Red|>|>; ResourceFunction["AssociationMapAt"][f, testAssoc, {All, "Color"}]
Out[2]=

Apply a function to “ragged” parts of a nested association:

In[3]:=
ResourceFunction["AssociationMapAt"][f, testAssoc, {All, "Density"}]
Out[3]=

Apply a function to a part that doesn’t exist:

In[4]:=
ResourceFunction["AssociationMapAt"][f, testAssoc, {4}]
Out[4]=

Scope (1) 

The second argument of AssociationMapAt need not strictly be a nested association:

In[5]:=
ResourceFunction["AssociationMapAt"][f, g[<|a -> 1|>, b -> <||>], {All, Key[a]}]
Out[5]=
In[6]:=
ResourceFunction[ "AssociationMapAt"][f, <|a -> g[x, y], b -> <||>|>, {Key[a], 1}]
Out[6]=

Properties and Relations (1) 

Contrast the behavior of MapAt and AssociationMapAt:

In[7]:=
MapAt[f, <|"a" -> <||>, "b" -> <|"x" -> 1|>|>, {All, "x"}]
Out[7]=
In[8]:=
ResourceFunction[ "AssociationMapAt"][f, <|"a" -> <||>, "b" -> <|"x" -> 1|>|>, {All, "x"}]
Out[8]=

Requirements

Wolfram Language 11.3 (March 2018) or above

Version History

  • 1.0.0 – 04 December 2018

License Information