This is documentation for Mathematica 3, which was
based on an earlier version of the Wolfram Language.
 MapAt MapAt[ f , expr , n ] applies f to the element at position n in expr. If n is negative, the position is counted from the end. MapAt[ f , expr , i , j , ... ] applies f to the part of expr at position i , j , ... . MapAt[ f , expr , , , ... , , , ... , ... ] applies f to parts of expr at several positions. Example: MapAt[f, a, b, c , 2]. MapAt[f, a, b, c, d , 1 , 4 ]. MapAt[ f , expr , i , j , ... ] or MapAt[ f , expr , i , j , ... ] applies f to the part expr [[ i , j , ... ]]. MapAt[ f , expr , , , ... , , , ... , ... ] applies f to parts expr [[ , , ... ]], expr [[ , , ... ]], ... . The list of positions used by MapAt is in the same form as is returned by the function Position. MapAt applies f repeatedly to a particular part if that part is mentioned more than once in the list of positions. Example: MapAt[f, a, b, c , 1 , 3 , 1 ]. See the Mathematica book: Section 2.2.4. See also: ReplacePart, Delete, FlattenAt. Further Examples This specifies that f is mapped across the list at position 2 only. In[1]:= Out[1]= Here, f is mapped on the first position of the second element. In[2]:= Out[2]= To avoid ambiguity, you must put each part specification in a list, even when it involves only one index. In[3]:= Out[3]=