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Re: Map onto a column

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125498] Re: Map onto a column
  • From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
  • Date: Thu, 15 Mar 2012 00:36:33 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

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?





Try this:



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

a//MatrixForm



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



(1            2              3

4              5              6

7              8              9)





Map[f,Transpose[a][[2]]]



{f[2],f[5],f[8]}



Have fun.



Alexei BOULBITCH, Dr., habil.

IEE S.A.

ZAE Weiergewan,

11, rue Edmond Reuter,

L-5326 Contern, LUXEMBOURG



Office phone :  +352-2454-2566

Office fax:       +352-2454-3566

mobile phone:  +49 151 52 40 66 44



e-mail: alexei.boulbitch at iee.lu<mailto:alexei.boulbitch at iee.lu>








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