R how to change one of the level to NA

Question

I have a data set and one of its column has factor levels \"a\" \"b\" \"c\" \"NotPerformed\". How can I change all the \"NotPerformed\" factors to

Answer 1

Or simply use the inbuilt exclude option, which works regardless of whether the initial variable is a character or factor.

x <- c("a", "b", "c", "NotPerformed")

factor(x, exclude = "NotPerformed")
[1] a    b    c    
Levels: a b c

factor(factor(x), exclude = "NotPerformed")
[1] a    b    c    
Levels: a b c