Length of columns excluding NA in r

Question

Suppose that I have a data.frame as follows:

   a  b c
1  5 NA 6
2 NA NA 7
3  6  5 8

I would like to find the length of each column, excluding NA's. The answer should look like

a b c 
2 1 3 

So far, I've tried:

 !is.na()                  # Gives TRUE/FALSE
 length(!is.na())          # 9 -> Length of the whole matrix
 dim(!is.na())             # 3 x 3 -> dimension of a matrix
 na.omit()                 # removes rows with any NA in it.

Please tell me how can I get the required answer.

Answer 1

Or faster :

colSums(!is.na(dat))
a b c 
2 1 3 

Answer 2

> apply(dat, 2, function(x){sum(!is.na(x))})
a b c 
2 1 3 

Answer 3

Though the sum is probably a faster solution, I think that length(x[!is.na(x)]) is more readable.