Basic Examples

ValueMapIndexed
with a symbolic function
f
applied to a list of strings:
[◼]
ValueMapIndexed
[f,{"a","ab","abc"}]
In[]:=
f[a,{1}]a,f[ab,{2}]ab,f[abc,{3}]abc
Out[]=
Creates an association where each key is a hash of a value from a given list and position of that value in the list:
[◼]
ValueMapIndexed
[Hash[{##},"CRC32","HexString"]&,{"a","ab","ab","abc"}]
In[]:=
fabe700ea,d07e5997ab,d1bc33a0ab,985de15aabc
Out[]=

Scope

ValueMapIndexed
works on the first level of expressions:
[◼]
ValueMapIndexed
[f,IdentityMatrix[3]]
In[]:=
f[{1,0,0},{1}]{1,0,0},f[{0,1,0},{2}]{0,1,0},f[{0,0,1},{3}]{0,0,1}
Out[]=
It can be made to work on lower levels by using
Map
in conjunction with
ValueMapIndexed
:
Map
[◼]
ValueMapIndexed
[f],IdentityMatrix[3]
In[]:=
{f[1,{1}]1,f[0,{2}]0,f[0,{3}]0,f[0,{1}]0,f[1,{2}]1,f[0,{3}]0,f[0,{1}]0,f[0,{2}]0,f[1,{3}]1}
Out[]=
ValueMapIndexed works with
Query
on datasets:
Query
[◼]
ValueMapIndexed
[#1-ConstantArray[#2,Length[#1]]&][Dataset[{{3,4},{5,6}}]]
In[]:=
Out[]=
It also works with implicit
Query
operations :
Dataset[{{3,4},{5,6}}]
[◼]
ValueMapIndexed
[f]
In[]:=
Out[]=

Applications

Create integer row headers for the Paul Revere social network:
Query
[◼]
ValueMapIndexed
[#2[[1]]&][ResourceData["Paul Revere's Social Network in Colonial Boston"]]
In[]:=
Out[]=

Properties and Relations

The ValueMap resource function is a special case of
ValueMapIndexed
in which one ignores the index argument:
[◼]
ValueMapIndexed
[f[#1]&,{a,b,c,d}]===
[◼]
ValueMap
[f[#1]&,{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:
[◼]
ValueMapIndexed
[Length[#2]&,{"a","b"}]
In[]:=
1b
Out[]=
ValueMapIndexed
will not work properly on datasets without the use of query:
[◼]
ValueMapIndexed
[f][Dataset[{{2,3},{4,5}}]]
In[]:=

Neat Examples