How to convert two factors to adjacency matrix in R?

Question

I have a data frame with two columns (key and value) where each column is a factor:

df = data.frame(gl(3,4,labels=c('a','b','c')), gl(6,2))
colnames(df) = c("key", "value")
   key value
1    a     1
2    a     1
3    a     2
4    a     2
5    b     3
6    b     3
7    b     4
8    b     4
9    c     5
10   c     5
11   c     6
12   c     6

I want to convert it to adjacency matrix (in this case 3x6 size) like:

  1 2 3 4 5 6
a 1 1 0 0 0 0
b 0 0 1 1 0 0
c 0 0 0 0 1 1

So that I can run clustering on it (group keys that have similar values together) with either kmeans or hclust.

Closest that I was able to get was using model.matrix( ~ value, df) which results in:

   (Intercept) value2 value3 value4 value5 value6
1            1      0      0      0      0      0
2            1      0      0      0      0      0
3            1      1      0      0      0      0
4            1      1      0      0      0      0
5            1      0      1      0      0      0
6            1      0      1      0      0      0
7            1      0      0      1      0      0
8            1      0      0      1      0      0
9            1      0      0      0      1      0
10           1      0      0      0      1      0
11           1      0      0      0      0      1
12           1      0      0      0      0      1

but results aren't grouped by key yet.

From another side I can collapse this dataset into groups using:

aggregate(df$value, by=list(df$key), unique)
  Group.1 x.1 x.2
1       a   1   2
2       b   3   4
3       c   5   6

But I don't know what to do next...

Can someone help to solve this?

Answer 1

An easy way to do it in base R:

res <-table(df)
res[res>0] <-1
res
   value
#key 1 2 3 4 5 6
#  a 1 1 0 0 0 0
#  b 0 0 1 1 0 0
#  c 0 0 0 0 1 1