Thanks Duncan,
Comments and a proposed bug fix in-line below:
-----Original Message-----
From: Duncan Murdoch [mailto:murdoch at stats.uwo.ca]
Sent: Wednesday, April 29, 2009 5:10 PM
To: Steven McKinney
Cc: R-help at r-project.org
Subject: Re: [R] Corrupt data frame construction - bug?
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.
I did some more digging on '$' - there is a data.frame method for it:
getAnywhere("$<-.data.frame" )
A single object matching '$<-.data.frame' was found
It was found in the following places
package:base
registered S3 method for $<- from namespace base
namespace:base
with value
function (x, i, value)
{
cl <- oldClass(x)
class(x) <- NULL
nrows <- .row_names_info(x, 2L)
if (!is.null(value)) {
N <- NROW(value)
if (N > nrows)
stop(gettextf("replacement has %d rows, data has %d",
N, nrows), domain = NA)
if (N < nrows && N > 0L)
if (nrows%%N == 0L && length(dim(value)) <= 1L)
value <- rep(value, length.out = nrows)
else stop(gettextf("replacement has %d rows, data has %d",
N, nrows), domain = NA)
if (is.atomic(value))
names(value) <- NULL
}
x[[i]] <- value
class(x) <- cl
return(x)
}<environment: namespace:base>
I placed a browser() command before return(x) and did some poking
around.
It seems to me there's a bug in this function. It should be able to
detect the problem I threw at it, and throw an error as you point out is
thrown by the other data.frame assign method.
I modified the rows
if (N < nrows && N > 0L)
if (nrows%%N == 0L && length(dim(value)) <= 1L)
to read
if (N < nrows)
if (N > 0L && nrows%%N == 0L && length(dim(value)) <= 1L)
as in
"$<-.data.frame" <-
function (x, i, value)
{
cl <- oldClass(x)
class(x) <- NULL
nrows <- .row_names_info(x, 2L)
if (!is.null(value)) {
N <- NROW(value)
if (N > nrows)
stop(gettextf("replacement has %d rows, data has %d",
N, nrows), domain = NA)
if (N < nrows)
if (N > 0L && nrows%%N == 0L && length(dim(value)) <= 1L)
value <- rep(value, length.out = nrows)
else stop(gettextf("replacement has %d rows, data has %d",
N, nrows), domain = NA)
if (is.atomic(value))
names(value) <- NULL
}
x[[i]] <- value
class(x) <- cl
return(x)
}
Now it detects the problem I created, in the fashion you demonstrated
above for the replacement using data.frame().
Error in `$<-.data.frame`(`*tmp*`, "NewCol", value = integer(0)) :
replacement has 0 rows, data has 3
It doesn't appear to stumble on weird data frames (these from the
?data.frame help page)
Error in `$<-.data.frame`(`*tmp*`, "NewCol", value = integer(0)) :
replacement has 0 rows, data has 10
### Catches this problem above alright.
d.0$NewCol <- foo[foo[, 1] == 4, 4]
d.0
[1] x y fac NewCol
<0 rows> (or 0-length row.names)
### Lets the above one through alright.
d00$NewCol <- foo[foo[, 1] == 4, 4]
d00
[1] NewCol
<0 rows> (or 0-length row.names)
### Lets the above one through alright.
Would the above modification work to fix this problem?
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