I have the following data.table:
dt <- data.table(col1 = rep("a",6), col2 = c(1,1,1,2,3,1))
dt$col2[dt$col2==1,] <- "bigDog"
Had you not wanted to change the type of the column, you'd do:
dt[col2 == 1, col2 := 123]
With the type change, you can do:
dt[, col2 := as.character(col2)][col2 == "1", col2 := "bigDog"]
If you don't change the type first, "bigDog" will get coerced to integer, i.e.
NA. You'll also get a bunch of warnings about that of course.
Note that besides less cumbersome syntax, using
:= has the advantage of not making extra copies of data (as
<- will) and instead modifies in place.