CODEWITHSUNDEEP
rvectorsequence
soy-ish
soy-ish

Reputation: 35

R - Grabbing the index of the first occurrence of a value after a refresh point?

Let's say I have a vector:

vec <- c(3,0,1,3,0,1,0,1,2,3,0,0,1,3,1,3)

I want to obtain the index of the first occurrence of 1 after every 3. So, the output of indices I want is

3,6,13,15

How would I do this in R?

Upvotes: 0

Views: 30

Answers (2)

akrun
akrun

Reputation: 887223

We can also use rleid

library(data.table)
na.omit(as.vector(tapply(seq_along(vec) * (vec== 1), rleid(vec == 3), FUN = function(x)x[x  > 0][1])))
#[1]  3  6 13 15

Upvotes: 0

Ian Campbell
Ian Campbell

Reputation: 24820

One approach would be to use cumsum to keep track of 3s.

mat <- cbind(cumsum(vec==3), vec == 1)
which(!duplicated(mat) & mat[,2] & mat[,1] > 0)
[1]  3  6 13 15

Upvotes: 2

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