Selective (or partial) sorting of vector elements in R

Question

I have a vector called myvec<- c("B","C","D","A") . I want to position C and D elements first and second then B and A .Thus the result should be C,D,B,A . How can we get this done in R?

Answer 1

To just bring "C" and "D" to the front:

myvec <- c("B","C","D","A")

myvec[order(!myvec %in% c('C', 'D'))]
#[1] "C" "D" "B" "A"

To give a complete ordering:

myvec <- c("B","C","D","A")

order.vec <- c('C', 'D', 'B', 'A')

myvec[order(match(myvec, order.vec))]
# [1] "C" "D" "B" "A"

Example with a different input vector:

myvec <- sample(myvec, 20, T)

myvec[order(match(myvec, order.vec))]
# [1] "C" "C" "C" "C" "C" "C" "D" "D" "D" "D" "D" "D" "B" "B" "B" "A" "A" "A" "A" "A"

Answer 2

You can using factor

 sort(factor(myvec <- sample(myvec, 20, T),c('C', 'D', 'B', 'A')))
 [1] C C C D D D D D D B B B B B B A A A A A
Levels: C D B A

Answer 3

I generally use setdiff() for when I want to remove elements from a vector

myvec <- c("B","C","D","A")
put_first <- c("C", "D")
new_vec <- c(put_first, setdiff(myvec, put_first))
new_vec
# [1] "C" "D" "B" "A"

Edited If you want it to allow for multiples in the data.

myvec <- c("B", "B","C", "C","D", "D", "A", "A")
put_first <- c("C", "D")
new_vec <- c(myvec[myvec %in% put_first], myvec[!myvec %in% put_first])
new_vec
# [1] "C" "C" "D" "D" "B" "B" "A" "A"