Basic Examples

Create keys by mapping symbolic function
f
over a list of strings:
[◼]
ValueMap
[f,{"a","ab","abc"}]
In[]:=
f[a]a,f[ab]ab,f[abc]abc
Out[]=
Create an association between hashes of the values and the values themselves:
[◼]
ValueMap
[Hash[#,"CRC32","HexString"]&,{"a","ab","abc"}]
In[]:=
e8b7be43a,9e83486dab,352441c2abc
Out[]=

Scope

ValueMap works on the first level of expressions:
[◼]
ValueMap
[f,IdentityMatrix[3]]
In[]:=
f[{1,0,0}]{1,0,0},f[{0,1,0}]{0,1,0},f[{0,0,1}]{0,0,1}
Out[]=
Work on lower levels by using
Map
in conjunction with ValueMap:
Map
[◼]
ValueMap
[f],IdentityMatrix[3]
In[]:=
{f[1]1,f[0]0,f[0]0,f[1]1,f[0]0,f[1]1}
Out[]=
ValueMap works with
Query
on datasets:
Query
[◼]
ValueMap
[Total][Dataset[{{3,4},{5,6}}]]
In[]:=
7
{3,4}
11
{5,6}
Out[]=
It also works with implicit
Query
operations :
Dataset[{{3,4},{5,6}}]
[◼]
ValueMap
[Total]
In[]:=
7
{3,4}
11
{5,6}
Out[]=

Applications

Create row headers for the Paul Revere social network based on the name of the person involved:
Query
[◼]
ValueMap
[#Name&][ResourceData["Paul Revere's Social Network in Colonial Boston"]]
In[]:=
Out[]=

Properties and Relations

One can accomplish much the same thing as ValueMap with the following code that uses
AssociationMap
; however, it is quite cumbersome:
Association[KeyValueMap[Rule@@Reverse[{#1,#2}]&,AssociationMap[f,{a,b,c,d}]]]===
[◼]
ValueMap
[f,{a,b,c,d}]
In[]:=
True
Out[]=

Possible Issues

If the keys generated from application of the function are not unique, the value for that key will be the last value encountered that generated the key:
[◼]
ValueMap
[StringLength,{"a","b"}]
In[]:=
1b
Out[]=
Sometimes, this deletion of key - value pairs with duplicate keys may be exactly what is desired, however:
[◼]
ValueMap
[Hash[#,"CRC32","HexString"]&][{Association["first""John","last""Smith"],Association["first""Mary","last""Jones"],Association["first""John","last""Smith"](*amistakenduplicate*)}]
In[]:=
b6493968firstJohn,lastSmith,132611e6firstMary,lastJones
Out[]=
ValueMap will not work properly on datasets without the use of
Query
:
[◼]
ValueMap
[f][Dataset[{{2,3},{4,5}}]]
In[]:=

f[{2,3}]
f[{4,5}]

2
3
4
5

Out[]=

Neat Examples

Use ValueMap to create a custom index on the hash of a function of two columns of a dataset and then use the index to swiftly retrieve information: