# Re: [R] ifelse on data frames

From: talepanda <talepanda_at_gmail.com>
Date: Fri 05 Jan 2007 - 07:38:05 GMT

> class(A)

[1] "data.frame"
> length(A)

[1] 5
> class(A==0)

[1] "matrix"
> length(A==0)

[1] 10
> class(-A*log(A))

[1] "data.frame"
> length(-A*log(A))

[1] 5

as you can see, the result of A==0 is matrix with length=10, while the result of -A*log(A) is still data.frame with length=5.

then, when calling ifelse( [length=10], 0, [length=5] ), internally, the NO(3rd) argument was repeated by rep(-A*log(A),length.out=10) (try this).
the result is "list" with length=10 and each element has 2 sub-elements.

So, the return value of A[(A==0)==FALSE] has 2 sub-elements as you get.

I think what confusing you is the behavior of A==0.

However, when using 'ifelse', I think you should use matrix as the arguments because data.frame is not consistent with the purpose of 'ifelse'.

On 1/5/07, maj@stats.waikato.ac.nz <maj@stats.waikato.ac.nz> wrote:
> [Using R 2.2.0 on Windows XP; OK, OK, I will update soon!]
>
> I have noticed some undesirable behaviour when applying
> ifelse to a data frame. Here is my code:
>
> A <- scan()
> 1.000000 0.000000 0.000000 0 0.00000
> 0.027702 0.972045 0.000253 0 0.00000
>
> A <- matrix(A,nrow=2,ncol=5,byrow=T)
> A == 0
> ifelse(A==0,0,-A*log(A))
>
> A <- as.data.frame(A)
> ifelse(A==0,0,-A*log(A))
>
> and this is the output:
>
> > A <- scan()
> 1: 1.000000 0.000000 0.000000 0 0.00000
> 6: 0.027702 0.972045 0.000253 0 0.00000
> 11:
> > A <- matrix(A,nrow=2,ncol=5,byrow=T)
> > A == 0
> [,1] [,2] [,3] [,4] [,5]
> [1,] FALSE TRUE TRUE TRUE TRUE
> [2,] FALSE FALSE FALSE TRUE TRUE
> > ifelse(A==0,0,-A*log(A))
> [,1] [,2] [,3] [,4] [,5]
> [1,] 0.00000000 0.00000000 0.000000000 0 0
> [2,] 0.09934632 0.02756057 0.002095377 0 0
> >
> > A <- as.data.frame(A)
> > ifelse(A==0,0,-A*log(A))
> [[1]]
> [1] 0.00000000 0.09934632
>
> [[2]]
> [1] NaN 0.02756057
>
> [[3]]
> [1] 0
>
> [[4]]
> [1] NaN NaN
>
> [[5]]
> [1] 0
>
> [[6]]
> [1] 0.00000000 0.09934632
>
> [[7]]
> [1] 0
>
> [[8]]
> [1] 0
>
> [[9]]
> [1] 0
>
> [[10]]
> [1] 0
>
> >
>
> Is this a bug or a feature? Can the behaviour be explained?
>
> Regards, Murray Jorgensen
> --
> Dr Murray Jorgensen http://www.stats.waikato.ac.nz/Staff/maj.html
> Department of Statistics, University of Waikato, Hamilton, New Zealand
> Email: maj@waikato.ac.nz Fax 7 838 4155
> Phone +64 7 838 4773 wk Home +64 7 825 0441 Mobile 021 1395 862
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri Jan 05 21:53:56 2007

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