replace a list of values by another in R

Question

I have a dataframe with any of these values.

from=c(\"A\",\"C\",\"G\",\"T\",\"R\",\"Y\",\"M\",\"K\",\"W\", \"S\",\"N\")

and I want to replace a

Answer 1

Create a map

map = setNames(to, from)

and go from A to B

dd[] = map[dd]

The map serves as a look-up, associating 'from' names with 'to' values. The assignment preserves matrix dimensions and dimnames.

Answer 2

matrix(to[match(dd,from)], nrow=nrow(dd))

match returns a vector without dimensions, so you need to recreate the matrix.

Answer 3

I used a similar for loop as OP and timed the solutions. Theodore's one is fastest by a slight margin, but Martin's is very readable.

dd<-matrix(sample(from, 100, replace = TRUE),10,10)
ddr <- dd
ddm <- dd
ddt <- dd

benchmark(roman = {
  for (i in 1:length(from)) {
    ddr[ddr == from[i]] <- to[i]
  }},
  martin = {
    map = setNames(to, from)
    ddm[] = map[dd]
  },
theodore = {ddt <- matrix(to[match(dd,from)], nrow=nrow(dd))},
          replications = 100000
)
      test replications elapsed relative user.self sys.self user.child sys.child
2   martin       100000    1.93    1.191      1.91        0         NA        NA
1    roman       100000    8.23    5.080      8.11        0         NA        NA
3 theodore       100000    1.62    1.000      1.61        0         NA        NA