How to find the index of an element in a vector in R?

There are three ways to find the index of an element in a vector.

Example

> x <- sample(1:10)
> x
[1] 8 10 9 6 2 1 4 7 5 3

Using which

> which(x == 6)[[1]]
[1] 4

Here we found the index of 6 in vector x.

Using match

> match(c(4,8),x)
[1] 7 1

Here we found the index of 4 and 8 in vector x.

Using which with %in%
> which(x %in% c(2,4))
[1] 5 7

Here we found the index of 2 and 4 in vector x.