Rescale Vector R

Question

Suppose I have a vector of integers such as:

> x
[1]  1  1  1  4  4 13 13 14

I am looking for an efficient way in R to rescale the vector to integers 1 to the max of the unique number of elements. Therefore the resulting vector would be:

1 1 1 2 2 3 3 4

Seems like a simple problem but I'm having trouble finding an efficient way to do it. In practice this vector is large (around 500).

Answer 1

Try match(x, sort(unique(x))):

x <- sample(1:50, 1e6, replace = TRUE)
benchmark(as.integer(factor(x)), match(x, sort(unique(x))),
          replications = 20, columns = c("test", "elapsed", "relative"))
#                        test elapsed relative
# 1     as.integer(factor(x))   18.44    10.36
# 2 match(x, sort(unique(x)))    1.78     1.00

identical(as.integer(factor(x)), match(x, sort(unique(x))))
# [1] TRUE

Answer 2

Try the following command, assuming that v is your vector

rank( v )

see ?rank for more information.

Well, this does give another result, but is correct as ranking, which is what I thought you want to achieve. To get your preferred result, do

as.integer( factor( v ) )