# R: How to count length of intervals between specific word/symbol in a vector?

I have a vector that contains series of texts and numbers, like:

``````t <- c("A", 1:3, "A", 1:4, "A", 1:3)
t
#>   "A" "1" "2" "3" "A" "1" "2" "3" "4" "A" "1" "2" "3"
``````

Created on 2022-08-06 by the reprex package (v2.0.1)

That is, the actual data is taken from a pdf, with the data frame collapsed into a single column vector, and the wrap length is uneven for some reason (probably because of the cell merging).
To process this data efficiently, I want to know the length from "A" to next "A" or end. In this example the answer would be 3, 4, 3 (Edit: sorry for a simple mistake, it would be 4, 5, 4).
I have tried many different methods but can’t find one that works. Does anyone know of a better way?

### >Solution :

You want the number of elements

• (2) from the last "A" (excluding it) to the end.

We can use either of the following:

``````diff(c(which(t == "A"), length(t) + 1)) - 1
# 3 4 3

diff(which(c(t, "A") == "A")) - 1
# 3 4 3
``````

Essentially we pad an "A" at the end to turn (2) into (1). If the last element of `t` happens to be an "A", the last value in the result will be 0.

Extension:

If you further want to know the number of elements from the beginning to the first "A" (excluding it), we can pad a leading "A":

``````diff(c(0, which(t == "A"), length(t) + 1)) - 1
# 0 3 4 3

diff(which(c("A", t, "A") == "A")) - 1
# 0 3 4 3
``````

Here, the first value is 0, because the first element of `t` happens to be an "A".