Sort vector of integers in specific (custom) order

A somewhat convoluted option:

x[order(factor(x,levels = c(2,1,3)))]

or obviously, just the order call for just the indices.

A simple remapping of the values works:

x <- sample(1:3, 10, replace=T)
x
 [1] 2 3 1 1 3 2 2 3 3 2
order(c(2,1,3)[x])
 [1]  1  6  7 10  3  4  2  5  8  9