Re: Matrix Element Extraction
- To: mathgroup at smc.vnet.net
- Subject: [mg46637] Re: Matrix Element Extraction
- From: bobhanlon at aol.com (Bob Hanlon)
- Date: Thu, 26 Feb 2004 17:53:25 -0500 (EST)
- References: <c1irc0$6bn$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Select[Position[mat, _Integer, 2],
#[[1]] == Length[mat] ||
#[[2]] == Length[mat[[1]]] &]
Bob Hanlon
In article <c1irc0$6bn$1 at smc.vnet.net>, "Curt Fischer" <crf3 at po.cwru.edu>
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.)