[R] ifelse choices in a data.frame?

[jim holtman]

use ifelse:

> DF <- data.frame(cbind(a=1:4, b=1:2, c=1:8, d=1:16, e=0, f=0))
> DF$Test <- with(DF, a == b)
>
> DF$e = (DF$c*DF$d) * DF$Test + (DF$c+DF$d) * !DF$Test
>
> DF$f = with(DF, (c*d)*Test + (c+d)*!Test)
> #or
> DF$f.1 <- ifelse(DF$Test, DF$c * DF$d, DF$c + DF$d)
> head(DF)
  a b c d  e  f  Test f.1
1 1 1 1 1  1  1  TRUE   1
2 2 2 2 2  4  4  TRUE   4
3 3 1 3 3  6  6 FALSE   6
4 4 2 4 4  8  8 FALSE   8
5 1 1 5 5 25 25  TRUE  25
6 2 2 6 6 36 36  TRUE  36
>


On Sun, Jul 19, 2009 at 5:17 PM, Mark Knecht<markknecht at gmail.com> wrote:
> Hi,
>   In my data.frame I  wanted to essentially write
>
> If(Test) c*d else c+d
>
> but that doesn't work. I found I could do it mathematically, but it
> seems forced and won't scale well for nested logic. I have two
> examples below writing columns e & f, but I don't think the code is
> self-documenting as it depends on knowing that Test is a TRUE/FALSE.
>
>   Is there a better way to do the following?
>
> Thanks,
> Mark
>
>
> DF <- data.frame(cbind(a=1:4, b=1:2, c=1:8, d=1:16, e=0, f=0))
> DF$Test <- with(DF, a == b)
>
> DF$e = (DF$c*DF$d) * DF$Test + (DF$c+DF$d) * !DF$Test
>
> DF$f = with(DF, (c*d)*Test + (c+d)*!Test)
>
> DF
>
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>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

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