On 29/04/2009 6:41 PM, Steven McKinney wrote:> Hi useRs,
>
> A recent coding infelicity along these lines
> yielded a corrupt data frame.
>
> foo <- matrix(1:12, nrow = 3)
> bar <- data.frame(foo)
> bar$NewCol <- foo[foo[, 1] == 4, 4]
> bar
> lapply(bar, length)
>
>
>
>
>> foo <- matrix(1:12, nrow = 3)
>> bar <- data.frame(foo)
>> bar$NewCol <- foo[foo[, 1] == 4, 4]
>> bar
> X1 X2 X3 X4 NewCol
> 1 1 4 7 10 <NA>
> 2 2 5 8 11 <NA>
> 3 3 6 9 12 <NA>
> Warning message:
> In format.data.frame(x, digits = digits, na.encode = FALSE) :
> corrupt data frame: columns will be truncated or padded with NAs
>> lapply(bar, length)
> $X1
> [1] 3
>
> $X2
> [1] 3
>
> $X3
> [1] 3
>
> $X4
> [1] 3
>
> $NewCol
> [1] 0
>
>
> Is this a bug in the data.frame machinery?
> If an attempt is made to add a new column
> to a data frame, and the new object does
> not have length = number of rows of data frame,
> or cannot be made to have such length via recycling,
> shouldn't an error be thrown?
>
> Instead in this example I end up with a
> "corrupt data frame" having one zero-length column.
>
>
> Should this be reported as a bug, or did I misinterpret
> the documentation?
I don't think "$" uses any data.frame machinery. You are working
at a
lower level.
If you had added the new column using
bar <- data.frame(bar, NewCol=foo[foo[, 1] == 4, 4])
you would have seen the error:
Error in data.frame(bar, NewCol = foo[foo[, 1] == 4, 4]) :
arguments imply differing number of rows: 3, 0
But since you treated it as a list, it let you go ahead and create
something that was labelled as a data.frame but wasn't. This is one of
the reasons some people prefer S4 methods: it's easier to protect
against people who mislabel things.
Duncan Murdoch
>
>
>
>
>> sessionInfo()
> R version 2.9.0 (2009-04-17)
> powerpc-apple-darwin8.11.1
>
> locale:
> en_CA.UTF-8/en_CA.UTF-8/C/C/en_CA.UTF-8/en_CA.UTF-8
>
> attached base packages:
> [1] stats graphics grDevices utils datasets methods base
>
> other attached packages:
> [1] nlme_3.1-90
>
> loaded via a namespace (and not attached):
> [1] grid_2.9.0 lattice_0.17-22 tools_2.9.0
>
>
> Also occurs on Windows box with R 2.8.1
>
>
>
> Steven McKinney
>
> Statistician
> Molecular Oncology and Breast Cancer Program
> British Columbia Cancer Research Centre
>
> email: smckinney +at+ bccrc +dot+ ca
>
> tel: 604-675-8000 x7561
>
> BCCRC
> Molecular Oncology
> 675 West 10th Ave, Floor 4
> Vancouver B.C.
> V5Z 1L3
> Canada
>
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