Count unique values for every column

Question

I would like to return the count of the unique values for every column in a table. For example, if I have the table:

 Testdata <- data.frame(var_1 = c(\"a         


        

Answer 1

You could use apply:

apply(Testdata, 2, function(x) length(unique(x)))
# var_1 var_2 var_3 
#     1     1     3

Answer 2

Here's an alternative:

aggregate(values ~ ind, unique(stack(Testdata)), length)
#     ind values
# 1 var_1      1
# 2 var_2      1
# 3 var_3      3

This requires the columns be character.