Question

I have a vector in R that looks like this:

dat <- c(TRUE, TRUE, FALSE, FALSE, TRUE, FALSE)

What I would like to calculate is the distance between a particular value and the subsequent occurrence of the same value. In the example I look for the subsequent occurrence of “TRUE” and I would like the resulting vector to be:

dat1 <- c(1, 3, NA, NA, NA, NA)

Is there an easy way to do this?

Answer 1

Why the NA values at the end?

You can get -in this case- the correct answer by:

> diff(which(X))
[1] 1 3

or, for the FALSE values :

> diff(which(!X))
[1] 1 2

You can then add as many NA values as you like, or predefine a vector, eg :

> result <- rep(NA,6)
> tmp <- diff(which(X))
> result[seq_along(tmp)] <- tmp
> result
[1]  1  3 NA NA NA NA