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

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

## Arguments

object

a somRes object.

init.graph

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

...

Not used.

## Value

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.

## References

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".

## Author

Madalina Olteanu olteanu@ceremade.dauphine.fr
Nathalie Vialaneix nathalie.vialaneix@inrae.fr

## Examples

data(lesmis)
set.seed(7383)
mis.som <- trainSOM(x.data=dissim.lesmis, type="relational", nb.save=10)
proj.lesmis <- projectIGraph(mis.som, lesmis)
if (FALSE) plot(proj.lesmis)