r Kohonen map - How to find position of one dataset?

Question

I have a dataframe df with my data of interest

I rescale with

df.sc <- scale(df)

and make my Kohonen map with

df.grid <- somgrid(15, 10, "hexagonal")
df.som <- som(df.sc, rlen=700, grid = df.grid)

That works fine and I get a nice map.

Now I have an extra datapoint

extra.sc <- as.matrix(-0.29985191, -0.35905786, -0.260923297, -0.2415673150,
 -0.259426676, -0.330404078)

It is scaled exactly the same way as df.sc

Now I want to see the position of the unit in the kohonen map given the df.som for the extra.sc

map(df.som,extra.sc)

does not give me what I want.

How can I determine the position of extra.sc within df.som? And preferentially also how I can mark it on the map

Answer 1

Maybe you defined your new data incorrectly, i.e. they did not have similar dimension with that of the training data. Check the output of extra.sc using parenthesis (extra.sc). I recommend that you provide the number of rows and columns to the definition of extra.sc using matrix() and c() function instead of as.matrix(). For example:

extra.sc <- matrix(c(0.29985191, -0.35905786, -0.260923297, -0.2415673150, -0.259426676, -0.330404078), nrow = 1, ncol = 6)`

and observe the result:

(extra.sc)

It is one row and six columns. If you do not provide the shape of your data, then R will regard them as one column and six rows.

extra.sc <- matrix(c(-0.29985191, -0.35905786, -0.260923297, -0.2415673150, -0.259426676, -0.330404078))

(extra.sc)