How to count TRUE values in a logical vector

Question

In R, what is the most efficient/idiomatic way to count the number of TRUE values in a logical vector? I can think of two ways:

z <- sample(c         


        

Answer 1

There are some problems when logical vector contains NA values.
See for example:

z <- c(TRUE, FALSE, NA)
sum(z) # gives you NA
table(z)["TRUE"] # gives you 1
length(z[z == TRUE]) # f3lix answer, gives you 2 (because NA indexing returns values)

So I think the safest is to use na.rm = TRUE:

sum(z, na.rm = TRUE) # best way to count TRUE values

(which gives 1). I think that table solution is less efficient (look at the code of table function).

Also, you should be careful with the "table" solution, in case there are no TRUE values in the logical vector. Suppose z <- c(NA, FALSE, NA) or simply z <- c(FALSE, FALSE), then table(z)["TRUE"] gives you NA for both cases.