r - Replace duplicated elements with NA, instead of removing them

Question

I have a DF. One of its columns looks like

DF$A
A
    a
    a
    a
    b
    b
    b
    c
    c

I am trying to replace all duplicated characters in this column with NA. Naively, I tried

DF$A <- DFl[duplicated(DF$A),] <- NA

But it just converts whole DF to NA values. Thank you for any suggestion.

Answer 1

You were pretty close. I'm not sure what DFl is though. But this works...

DF <- data.frame(A=c("a", "a", "a", "b", "b", "c"))
DF$A[duplicated(DF$A)] <- NA
> DF
     A
1    a
2 <NA>
3 <NA>
4    b
5 <NA>
6    c