Re: tab-delimited file to graph

*To*: mathgroup at smc.vnet.net*Subject*: [mg69469] Re: tab-delimited file to graph*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Wed, 13 Sep 2006 04:02:54 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <ee64q5$7s4$1@smc.vnet.net>

aitor69gonzalez at gmail.com wrote: > Hello, > > I have a directed graph "mygraph" in a tab delimited file that looks > like this: > v1 v2 > v2 v3 > v3 v1 > v1 v4 > I would like to import this graph into mathematica, so that I can take > advantage of the -DiscreteMath`Combinatorica`- functions. So far, I was > only able to import it with Import["mygraph","TSV"] into a list of > two-item lists. Now, I am stuck there. Can somebody help me to convert > this list of two-item lists into a matrix or adjacency list of a > directed graph? > > Thank you in advance, > > Aitor > Hi Aitor, Building an adjacency matrix from a list of pairs can be achieve with the function SparseArray. In the following, I will assume that the element of your list are literally named v1, v2, ..., vn. First we transform the pairs {vi,vj} into the pairs of numerical indices {i, j}. Then we build the replacement rules expected by SparseArray thanks to the function Thread. Finally, we build the matrix as a sparse array that contains 1 wherever two vertices are adjacent and 0 everywhere else. Note that a sparse array is a compact structure, highly efficient in terms of memory usage. You may want to see the sparse array as a regular dense matrix, however. You can do that by using the Normal function. lst = {{v1, v2}, {v2, v3}, {v3, v1}, {v1, v4}}; {v1, v2, v3, v4} = Range[4] --> {1, 2, 3, 4} lst --> {{1, 2}, {2, 3}, {3, 1}, {1, 4}} rls = Thread[lst -> Table[1, {Length[lst]}]] --> {{1, 2} -> 1, {2, 3} -> 1, {3, 1} -> 1, {1, 4} -> 1} SparseArray[rls]; MatrixForm[Normal[SparseArray[rls]]] --> 0 1 0 1 0 0 1 0 1 0 0 0 Best regards, Jean-Marc