[R] Is this an artifact of using "which"?

From: Tania Oh <tania.oh_at_bnc.ox.ac.uk>
Date: Mon, 14 Apr 2008 12:32:15 +0100


Dear all,

I used "which" to obtain a subset of values from my data.frame. however, I find that there is a "trace" of the values I have removed. Any suggestions would be greatly appreciate.

Below is my data:

d <- data.frame( val = 1:10,

                 group = sample(LETTERS[1:5], 10, repl=TRUE) )

 >d

    val group

1    1     B
2    2     E
3    3     B
4    4     C
5    5     A
6    6     B
7    7     A
8    8     E
9    9     E
10  10     A

## selecting everything that is not group "A"   d<-d[which(d$group !="A"),]

> d

   val group

1   1     B
2   2     E
3   3     B
4   4     C
6   6     B
8   8     E
9   9     E

> levels(d$group)

[1] "A" "B" "C" "E"

## why is group A still reflected here?

Many thanks in advance,
tania

D.phil student
Department of Physiology, Anatomy and Genetics Oxford University



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