Creating a 2 by 2 table with no values in one column or row in R

Question

I need to table my data to a 2*2 table, however, due to no values in some cells, the table command in R does not provide a column or row depending on the data. For example:

a<-matrix(c(0,1,1,1,1,1,1,1),4,2)
table(a[,1],a[,2])

This is how it presents:

  1
0 1
1 3

However, I need it to be like

  0  1
0 0  1
1 0  3

Any suggestion?

Answer 1

The problem is that your matrix a contains numbers and with numbers R has no chance to know which columns should be shown. The solution is though easy. You have to transform you data into a factor, where you provide all potential values:

table(factor(a[,1], levels = unique(c(a))),factor(a[,2], levels = unique(c(a))))
#   0 1
# 0 0 1
# 1 0 3