Count unique occurrences within data frame

Question

Let the table be as follows:

v1	v2	v3
A	B	A
B	B	A
	A	C
D	C	D

What i want R to create a table for number of occurences of unique values for each column:

v1	v2	v3
A	1	1
B	1	2
C	0	1
D	1	0

Answer 1

One option could be:

sapply(df, function(x) table(factor(x, levels = unique(unlist(df)))))

  V1 v2 v3
A  1  1  2
B  1  2  0
D  1  0  1
C  0  1  1