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Re: Map onto a column
*To*: mathgroup at smc.vnet.net
*Subject*: [mg125449] Re: Map onto a column
*From*: Bill Rowe <readnews at sbcglobal.net>
*Date*: Wed, 14 Mar 2012 00:40:03 -0500 (EST)
*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com
On 3/13/12 at 3:02 AM, slypandemia at gmail.com (Sly Pandemia) wrote:
>Is there a neat way to map a function onto a specific column in an
>array?
>For example if I have
>a = {{1,2,3},{4,5,6},{7,8,9}}
>and I want to map f onto the second element in each row. I would
>normally use
>b = Map[MapAt[f,#,2]&,a]
>but this seems a bit awkward. I would expect to be able to use
>b = MapAt[f,a,{All,2}]
>but this appears to be illegal syntax.
>Is there any way to do what I want with a single Map/MapAt function?
Here is one way. But I don't that it will be any more
satisfactory to you
MapAt[f, a, Table[{n, 2}, {n, 3}]]
And to show this is the same
In[4]:= MapAt[f, a, Table[{n, 2}, {n, 3}]] == Map[MapAt[f, #, 2]
&, a]
Out[4]= True
Or how about re-writing your solution as
MapAt[f,#,2]&/@a
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