R package Kohonen - how to plot hexagons instead of circles as in Matlab SOM toolbox?

Question

Is it possible to plot the SOM map (package Kohonen) with hexagons as elementary forms instead of circles? Now the different plottings (count, changes etc.) are plotted as

Answer 1

You can use Voronoi plots to get a space filled representation (hexagons).

• the hex grid coordinates are stored in $grid$pts of the kohonen object,
• the codes are in $codes

Putting this together with a lattice plot:

require ("kohonen")
require ("latticeExtra")
require ("deldir")
som.wines <- som (scale (wines), grid = somgrid(5, 5, "hexagonal"))

df <- as.data.frame (cbind (som.wines$grid$pts, som.wines$codes))
levelplot (alcohol ~ x * y, data = df, panel = panel.voronoi, aspect = "iso)

yields:

(I don't know for sure, but I guess that would have been possible already in 2010).