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Re: Map onto a column

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125463] Re: Map onto a column
  • From: Sseziwa Mukasa <mukasa at gmail.com>
  • Date: Wed, 14 Mar 2012 00:44:57 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201203130802.DAA12753@smc.vnet.net>

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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