[R] Infelicity in print output with matrix indexing of `[.data.frame`

[Bert Gunter]

It's documented, David:

>From ?"[.data.frame"

"Matrix indexing (x[i] with a logical or a 2-column integer matrix i)
using [ is not recommended. For extraction, x is first coerced to a
matrix..."

ergo characters for a mixed mode frame.

Cheers,
Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Sat, Dec 17, 2016 at 10:49 AM, David Winsemius
<dwinsemius at comcast.net> wrote:
> This puzzle started with an SO posting where the questioner showed output from a dataframe that had been indexed with a matrix. The output appeared to show that numeric values had been coerced to character. Once I got a reproducible example I discovered that the print output was the problem and that the actual values had not been coerced. I've created a much smaller test case and it appears from the testing below that a matrix indexed output from a dataframe with mixed numeric and character types will be printed as character even if none of the values indexed are character:
>
>> dat <- setNames( as.data.frame( matrix(1:12, ncol=4) ), LETTERS[1:4])
>> dat
>   A B C  D
> 1 1 4 7 10
> 2 2 5 8 11
> 3 3 6 9 12
>> dat[2,4]<-NA
>> dat[3,3]<-NA
>> ng <- which(is.na(dat), arr.ind=TRUE)
>> ng
>      row col
> [1,]   3   3
> [2,]   2   4
>> dat[ng] <- 20
>> dat[ng]
> [1] 20 20
>
> That was as expected. Now repeat the process with a dataframe of mixed types.
>
>> dat[2,4]<-NA
>> dat[3,3]<-NA
>> dat[,1]<- "a"
>> dat
>   A B  C  D
> 1 a 4  7 10
> 2 a 5  8 NA
> 3 a 6 NA 12
>> dat[ng] <- 20
>> dat[ng]
> [1] "20" "20"
>
> Quoted print output was not what I was expecting.
>
> --
>
> David Winsemius
> Alameda, CA, USA
>
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