r - 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(TRUE, FALSE), 1000, rep = TRUE)
sum(z)
# [1] 498

table(z)["TRUE"]
# TRUE 
#  498 

Which do you prefer? Is there anything even better?

Answer 1

The safest way is to use sum with na.rm = TRUE:

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

which gives 1.

There are some problems with other solutions 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)

Additionally 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. See for example:

z <- c(FALSE, FALSE)
table(z)["TRUE"] # gives you `NA`

or

z <- c(NA, FALSE)
table(z)["TRUE"] # gives you `NA`