[R] ifelse on data frames

[Henric Nilsson]

maj at stats.waikato.ac.nz said the following on 2007-01-05 04:18:

> [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))

How about using

sapply(A, function(x) ifelse(x == 0, 0, -x*log(x)))

?


HTH,
Henric



> 
> 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:
> Read 10 items
>> 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