Re: creating adjacency matrices

*To*: mathgroup at smc.vnet.net*Subject*: [mg36591] Re: [mg36561] creating adjacency matrices*From*: Andrzej Kozlowski <andrzej at tuins.ac.jp>*Date*: Fri, 13 Sep 2002 01:14:09 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

First of all, Import is not really meant for this sort of situation; it is better to use ReadList. Suppose your file is: 1 A 1 B 2 B 3 C 4 B 5 D 5 E 6 F 7 A and its name is "adj.txt". Here is one way you can deal with this case. First, read in the file: In[1]:= ss=ReadList["adj.txt",{Number,Word}] Out[1]= {{1,A},{1,B},{2,B},{3,C},{4,B},{5,D},{5,E},{6,F},{7,A}} Next, find how many "actors" there are: In[2]:= l=Length[Union[First[Transpose[ss]]]] Out[2]= 7 Construct the adjacency matrix: In[3]:= Table[If[Intersection[Cases[ss,{i,x_}->x,{1}], Cases[ss,{j,x_}->x,{1}]]=!={},1,0](1-KroneckerDelta[i,j]),{i, l},{j,l}]//MatrixForm Out[3]//MatrixForm= 0 1 0 1 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 The function ToAdjacencyMatrix form the Combinatorica package constructs the adjacency matrix from a graph, so it has no direct application to your problem. Andrzej Kozlowski Toyama International University JAPAN On Thursday, September 12, 2002, at 02:27 am, Moliterno, Thomas wrote: > I need to create an adjacency matrix from my data, which is currently > in > the form of a .txt file and is basically a two column incidence list. > For example: > > 1 A > 1 B > 2 B > 3 C > . . > . . > . . > m n > > Where 1 to m represent actors and A to n represent events. My goal is > to > have an (m x m) matrix where cell i,j equals 1 if two actors are > incident to the same event (in the sample above, 1 and 2 are both > incident to B) and 0 otherwise (w/ zeros on the diagonal). > > I'm new to Mathmatica, and so I'm on the steep part of the learning > curve ... All I've been able to figure out so far is how to get my > incidence list into the program using Import["filename.txt"]. But then > what? How do I convert to the adjacency matrix? I've found the > ToAdjacencyMatrix[] command in DiscreteMath`Combinatorica`, but I can't > seem to get it to work ... > > Thanks to any and all in advance. > > Tom > > ********************************************** > Thomas P. Moliterno > Graduate School of Management > University of California, Irvine > tmoliter at uci.edu > ********************************************** > > >