[R] Am I misunderstanding the ifelse construction?

[Karin Lagesen]

I have a function like this:

changedir <- function(dataframe) {
dir <- dataframe$dir
gc_content <- dataframe$gc_content
d <- ifelse(dir == "-",
            gc_content <- -gc_content,gc_content <- gc_content)
return(d)
}

The goal of this function is to be able to input a data frame like this:


> lala
   dir gc_content
1    +        0.5
2    -        0.5
3    +        0.5
4    -        0.5
5    +        0.5
6    -        0.5
7    +        0.5
8    -        0.5
9    +        0.5
10   -        0.5
11   +        0.5
12   -        0.5
13   +        0.5
14   -        0.5
15   +        0.5
16   -        0.5
17   +        0.5
18   -        0.5
19   +        0.5
20   -        0.5
>

And change the sign of the value of the gc_content field if the
corresponding dir field is negative.

Howver, when I run this through the changedir function, all of the
gc_contents become negative.

An I misunderstanding how to use the ifelse construct? And in that
case, how should I go about doing this in a different way?

Thankyou very much in advance for your help, and I hope that my
question is not too banal!

Karin
-- 
Karin Lagesen, PhD student
karin.lagesen at medisin.uio.no
http://folk.uio.no/karinlag