Replace a value in a data frame based on a conditional (`if`) statement
In the R data frame coded for below, I would like to replace all of the times that B
appears with b.
junk <- data.frame(x <- rep(LETTERS[1:4], 3), y <- letters[1:12])
colnames(junk) <- c("nm", "val")
this provides:
nm val
1 A a
2 B b
3 C c
4 D d
5 A e
6 B f
7 C g
8 D h
9 A i
10 B j
11 C k
12 D l
My initial attempt was to use a for and if statements like so:
for(i in junk$nm) if(i %in% "B") junk$nm <- "b"
but as I am sure you can see, this replaces ALL of the values of junk$nm with b. I can see why this is doing this but I can't seem to get it to replace only those cases of junk$nm where the original value was B.
NOTE: I managed to solve the problem with gsub but in the interest of learning R I still would like to know how to get my original approach to work (if it is possible)
Answer
Easier to convert nm to characters and then make the change:
junk$nm <- as.character(junk$nm)
junk$nm[junk$nm == "B"] <- "b"
EDIT: And if indeed you need to maintain nm as factors, add this in the end:
junk$nm <- as.factor(junk$nm)