Compute the projection of a graph, provided as an igraph object, on the grid of the somRes object.

projectIGraph(object, init.graph, ...)



a somRes object.


an igraph whose number of vertices is equal to the clustering length of the somRes object.


Not used.


The result is an igraph which vertexes are the clusters (the clustering is thus understood as a vertex clustering) and the edges are the counts of edges in the original graph between two vertices corresponding to the two clusters in the projected graph or, if init.graph is a weighted graph, the sum of the weights between the pairs of vertices corresponding to the two clusters.

The resulting igraph object's attributes are:

  • the graph attribute layout which provides the layout of the projected graph according to the grid of the SOM;

  • the vertex attributes name and size which, respectively are the vertex number on the grid and the number of vertexes included in the corresponding cluster;

  • the edge attribute weight which gives the number of edges (or the sum of the weights) between the vertexes of the two corresponding clusters.


Olteanu M., Villa-Vialaneix N. (2015) Using SOMbrero for clustering and visualizing graphs. Journal de la Société Française de Statistique, 156, 95-119.

See also

projectIGraph.somSC which uses the results of a super-clustering to obtain another projected graph. plot.somRes with the option type="graph" or plot.somSC with the option type="projgraph".


Madalina Olteanu
Nathalie Vialaneix


mis.som <- trainSOM(, type="relational",
proj.lesmis <- projectIGraph(mis.som, lesmis)
if (FALSE) plot(proj.lesmis)