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Re: Map onto a column

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125492] Re: Map onto a column
  • From: Murta <rodrigomurtax at gmail.com>
  • Date: Thu, 15 Mar 2012 00:34:27 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201203130802.DAA12753@smc.vnet.net> <jjpbje$pbu$1@smc.vnet.net>

I agree that some solution like that

   b = MapAt[f,a,{All,2}]

would be much more elegant. Maybe in Mathematica 9??

On Mar 14, 2:50 am, Sseziwa Mukasa <muk... at gmail.com> wrote:
> Transpose the matrix and MapAt the appropriate row then Transpose back:
>
> Transpose[MapAt[f,Transpose[a],2]]
>
> On Mar 13, 2012, at 4:02 AM, 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?




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