Determine the number of NA values in a column

Question

I want to count the number of NA values in a data frame column. Say my data frame is called df, and the name of the column I am considering is col. The way I have come up with is the following:

sapply(df$col, function(x) sum(length(which(is.na(x)))))

Is this a good/most efficient way to do this?

Answer 1

To count the number of NA values in a column, you can use the sum() function as follows:

sum(is.na(df$col))

For example:

In the following data frame:

df <- data.frame(A = sample(c(1:20), 10),

                 B = sample(c(TRUE, FALSE,NA), 10, rep = TRUE))

df

    A     B

1   7    NA

2  12 FALSE

3   9  TRUE

4  11 FALSE

5  20    NA

6  17 FALSE

7   3    NA

8  10 FALSE

9  13    NA

10 18    NA

To count the number of NA values in column ‘B’:

 sum(is.na(df$B))

[1] 5