r - Get indexes of a vector of numbers in another vector

Question

Let's suppose we have the following vector:

v <- c(2,2,3,5,8,0,32,1,3,12,5,2,3,5,8,33,1)

Given a sequence of numbers, for instance c(2,3,5,8), I am trying to find what is the position of this sequence of numbers in the vector v. The result I expect is something like:

FALSE TRUE TRUE TRUE TRUE FALSE FALSE FALSE FALSE FALSE FALSE TRUE TRUE TRUE TRUE FALSE FALSE 

I am trying to use which(v == c(2,3,5,8)) but it doesn't give me what I am looking for.

Thanks beforehand.

Answer 1

Using base R you could do the following:

v <- c(2,2,3,5,8,0,32,1,3,12,5,2,3,5,8,33,1)
x <- c(2,3,5,8)

idx <- which(v == x[1])
idx[sapply(idx, function(i) all(v[i:(i+(length(x)-1))] == x))]
# [1]  2 12

This tells you that the exact sequence appears twice, starting at positions 2 and 12 of your vector v.

It first checks the possible starting positions, i.e. where v equals the first value of x and then loops through these positions to check if the values after these positions also equal the other values of x.