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

Set the level to NA:

x <- factor(c("a", "b", "c", "NotPerformed"))
x
## [1] a            b            c            NotPerformed
## Levels: a b c NotPerformed
levels(x)[levels(x)=='NotPerformed'] <- NA
x
## [1] a    b    c    
## Levels: a b c

Note that the factor level is removed.