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Re: Map onto one column of a matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95528] Re: Map onto one column of a matrix
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 21 Jan 2009 06:43:00 -0500 (EST)
  • Organization: Uni Leipzig
  • References: <gl49tb$g7v$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

data = {{a, b}, {c, d}};

MapAt[f, #, {-1}] & /@ data

data /. {q_, r_?AtomQ} :> {q, f[r]}

Regards
   Jens

. Grady wrote:
> Hi, suppose we've got a matrix
> 
> data = {{a, b}, {c, d}};
> 
> and we want to map a function onto just the second column, so we want
> to end up with
> 
> {{a, f[b]}, {c, f[d]}}.
> 
> The best way I've found to do this is with MapAt:
> 
> MapAt[f, data, Table[{i, 2}, {i, Length@data}]]
> 
> Is there a better way?  I keep hoping there's some notation similar to
> what's used in Part that lets you refer to a whole column with All,
> like data[[All,2]].  Thanks!
> 
> -Daniel
> 


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