Finding strings not %in% other vector of strings [duplicate]

Question

If you have a vector of strings and you want to know which match. It's a simple matter of using %in%.

x <- c("red","blue","green")
y <- c("yellow","blue","orange")

which(x %in% y) # Literally, which X are in Y.

But what about the opposite, where you would like to find which X are not in Y?

Answer 1

A neat way that I like (that I learnt from @joran, iirc) is:

`%nin%` <- Negate(`%in%`)
which(x %nin% y)
[1] 1 3    

Answer 2

Doing %in% returns a vector of trues and falses. Using an exclamation mark will turn those Ts and Fs around, and by wrapping everything in which will give you indices.

> which(!x %in% y)
[1] 1 3
> which(x %in% y)
[1] 2