Self-organizing map (SOM) example in R

SOM example.R

#SOM example using wines data set
library(kohonen)
data(wines)
set.seed(7)

#create SOM grid
sommap <- som(scale(wines), grid = somgrid(2, 2, "hexagonal"))

## use hierarchical clustering to cluster the codebook vectors
groups<-3
som.hc <- cutree(hclust(dist(sommap$codes)), groups)

#plot
plot(sommap, type="codes", bgcol=rainbow(groups)[som.hc])

#cluster boundaries
add.cluster.boundaries(sommap, som.hc)

Getting:

Error in dist(sommap$codes) :
(list) object cannot be coerced to type 'double'

any ideas?

Getting

Error in dist(sommap$codes) :
(list) object cannot be coerced to type 'double'

Any one to assist. Am a newbie in R

I tried this
som.hc <- cutree(hclust(dist(as.numeric(unlist(sommap$codes)))), groups)
for the error:
Error in dist(sommap$codes) :
(list) object cannot be coerced to type 'double'

and then no more error

but not sure if this is the correct way. I am a newbie too

following works

som.hc <- cutree(hclust(dist(sommap$codes[[1]])), groups)

i am a little confused about how to do clustering using the result of SOM...

How can you define the number of groups to be 3?

som.hc <- cutree(hclust(dist(sommap$codes[[1]])), groups)
thanks. this gives no error.

following works

som.hc <- cutree(hclust(dist(sommap$codes[[1]])), groups)

I follow yours suggested and it works