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]]]}