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Re: Map onto a column

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125478] Re: Map onto a column
  • From: Dana DeLouis <dana01 at me.com>
  • Date: Thu, 15 Mar 2012 00:29:35 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

> b = Map[MapAt[f,#,2]&,a]
> b = MapAt[f,a,{All,2}]   (...error)
> 
> Is there any way to do what I want with a single Map/MapAt function?

Hi.  Just another option:

m = {{1,2,3},{4,5,6},{7,8,9}};

m[[All,2]] = f/@m[[All,2]];
// or
m[[All,2]] = Map[f, m[[All,2]]]; 

m
{{1,f[2],3},{4,f[5],6},{7,f[8],9}}

= = = = = = = = = =
HTH  :>)
Dana DeLouis
Mac & Math 8
= = = = = = = = = =




On Mar 13, 4:04 am, Sly Pandemia <slypande... at gmail.com> 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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