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

which is good alternative, especially when you operate on matrices (check ?which and notice the arr.ind argument). But I suggest that you stick with sum, because of na.rm argument that can handle NA's in logical vector. For instance:

# create dummy variable
set.seed(100)
x <- round(runif(100, 0, 1))
x <- x == 1
# create NA's
x[seq(1, length(x), 7)] <- NA

If you type in sum(x) you'll get NA as a result, but if you pass na.rm = TRUE in sum function, you'll get the result that you want.

> sum(x)
[1] NA
> sum(x, na.rm=TRUE)
[1] 43

Is your question strictly theoretical, or you have some practical problem concerning logical vectors?