Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2009

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Map onto one column of a matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95558] Re: Map onto one column of a matrix
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Wed, 21 Jan 2009 06:48:37 -0500 (EST)

On 1/20/09 at 5:44 AM, D.C.Grady at gmail.com (D. Grady) wrote:

>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?

There are a variety of other ways. These include:

f[Last@#]&/@data  (* works since 2nd column is the last column *)

data/.{a_,b_}->{a,f[b]} (* for two column array *)

data/.{a_,b_,c__}->{a,f[b],c}  (* for n column array *)

Or if you like the data[[All,1]] construct and f has the
attribute Listable then

Transpose@{data[[All,1]],f[data[[All,2]]]}



  • Prev by Date: Re: image not displaying properly
  • Next by Date: Re: DO and LISTPLOT
  • Previous by thread: Re: Map onto one column of a matrix
  • Next by thread: Re: Map onto one column of a matrix