# 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,{{i1,j1,},{i2,j2,},}]

applies f to parts of expr at several positions.

MapAt[f,pos]

represents an operator form of MapAt that can be applied to an expression.

# Details • MapAt[f,expr,{i,j,}] or MapAt[f,expr,{{i,j,}}] applies f to the part expr[[i,j,]].
• MapAt[f,expr,{{i1,j1,},{i2,j2,},}] applies f to parts expr[[i1,j1,]], expr[[i2,j2,]], . »
• The list of positions used by MapAt is in the same form as is returned by the function Position. »
• MapAt works on Association objects, using the same specification for keys as in Part.
• MapAt applies f repeatedly to a particular part if that part is mentioned more than once in the list of positions. »
• MapAt[f,pos][expr] is equivalent to MapAt[f,expr,pos].

# Examples

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## Basic Examples(8)

Map f onto the part at position 2:

 In:= Out= Map f onto multiple parts:

 In:= Out= Map f onto a more deeply nested part:

 In:= Out= Map f onto the second element of all top-level parts (the "second column"):

 In:= Out= Map f onto an association:

 In:= Out= Use Key to specify position:

 In:= Out= For string keys, Key is not needed:

 In:= Out= Use negative position in an association:

 In:= Out= Use the operator form of MapAt:

 In:= Out= ## Possible Issues(1)

Introduced in 1988
(1.0)
|
Updated in 2014
(10.0)