R: Unselect matrix or data.frame columns by name

Question

Possible Duplicate:
Drop Columns R Data frame

Assuming a matrix with 3 named columns "A", "B", C", I can unselect columns "B" and "C" like this:

df[, -c(2, 3)]

But what if I want to use column names? How can I df[, -c("B", "C")]?

Agree it is duplicate. Comment: The -grep() strategy is more general. — IRTFM, Jan 05 '12 at 18:03

score 3 · Answer 1 · answered Jan 05 '12 at 17:02

3

Matching is your friend:

R> DF <- data.frame(A=1:2, B=2:3, C=3:4)
R> DF[, !(colnames(DF) %in% c("B","C")), drop=FALSE]
  A
1 1
2 2
R>

The key is that you need boolean vectors for indexing (or else, numeric indices). So any expression creating booleans will do.

answered Jan 05 '12 at 17:02

Dirk Eddelbuettel

Thanks, a lot more complicate than the - operator though :( – Robert Kubrick Jan 05 '12 at 17:32
So just define a new '-' (alike) operator or function. – Dirk Eddelbuettel Jan 05 '12 at 17:39
1

Good suggestion but then I'm not clear why it's not already defined. Why only for indexes? After all I can still use the column names to select columns: DF[, c("A", "B")] – Robert Kubrick Jan 05 '12 at 18:03

1 Answers1