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
______________________________________________
R-help@r-project.org 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.
______________________________________________
R-help@r-project.org 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.
