DonDyck - 4 months ago 27

R Question

I have a vector with some of the elements repeated. I want to list all the pairs of indices with equal values.

i.e. given input

`x <- c(1,2,3,2,4,3,2)`

I want to generate the list

`duplicate_x <- [[2,4,7],[3,6]]`

How to solve this in R

Answer

```
dups = duplicated(x) | duplicated(x, fromLast = T)
split(which(dups), x[dups])
#$`2`
#[1] 2 4 7
#
#$`3`
#[1] 3 6
```