R how many element satisfy a condition?

Question

Is there a better way to count how many elements of a result satisfy a condition?

a <- c(1:5, 1:-3, 1, 2, 3, 4, 5)
b <- c(6:-8)
u <- a > b
length         


        

Answer 1

If z consists of only TRUE or FALSE, then simply

length(which(z))

Answer 2

I've always used table for this:

a <- c(1:5, 1:-3, 1, 2, 3, 4, 5)
b <- c(6:-8)
table(a>b)
FALSE  TRUE 
    8     7 

Answer 3

sum does this directly, counting the number of TRUE values in a logical vector:

sum(u, na.rm=TRUE)

And of course there is no need to construct u for this:

sum(a > b, na.rm=TRUE)

works just as well. sum will return NA by default if any of the values are NA. na.rm=TRUE ignores NA values in the sum (for logical or numeric).