Re: Matrix Element Extraction

• To: mathgroup at smc.vnet.net
• Subject: [mg46634] Re: Matrix Element Extraction
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 26 Feb 2004 17:53:22 -0500 (EST)
• Organization: Universitaet Leipzig
• References: <c1irc0\$6bn\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,

I realy love your code but

Select[Position[mat, _Integer], Length[#] == 2 && MemberQ[#, 3] &]

may do what you want not only _mostly_
but it is not so wonderful cryptic :-(

Regards
Jens

Curt Fischer wrote:
>
> In a matrix, I want to find the positions of all the integer elements in the
> rightmost column or the bottom row.
>
> In[1]:=
> mat={{1,2,1},{4,5,6},{7,8,-Infinity}}
>
> Out[1]=
> {{1,2,1},{4,5,6},{7,8,-Infinity}}
>
> In[2]:=
> Position[Map[((MemberQ[Union[Flatten[{mat[[Length[mat]]],
>                 mat[[All,Dimensions[mat][[
>                       2]] ]]}]],#])&&(#!=-Infinity))&,mat,{2}],True]
>
> Out[2]=
> {{1,1},{1,3},{2,3},{3,1},{3,2}}
>
> This _mostly_ does what I want, but took me forever to think of.  I'm
> convinced there must be an easier way...
>
> Especially, is there an easy way to keep the point {1,1} from appearing on
> this
> list, other than using a replacement rule and an If[] command?  ({1,1} is
> not a position in the bottom row or right most column, so I don't want this
> point returned.)
>