Hi,
Two ways to create what should normally be the same data frame:
> df1 <- data.frame(a=character(0), b=character(0))> df1
[1] a b
<0 rows> (or 0-length row.names)
> df2 <- as.data.frame(matrix(character(0), ncol=2,
dimnames=list(NULL, letters[1:2])))
> df2
[1] a b
<0 rows> (or 0-length row.names)
unique() works as expected except that I get a warning on 'df2':
> unique(df1)
[1] a b
<0 rows> (or 0-length row.names)
> unique(df2)
[1] a b
<0 rows> (or 0-length row.names)
Warning message:
In is.na(rows) : is.na() applied to non-(list or vector) of type 'NULL'
Look like the two data frames are not identical:
> identical(df1, df2)
[1] FALSE
> all.equal(df1, df2)
[1] "Attributes: < Length mismatch: comparison on first 1 components >"
> attributes(df1)
$names
[1] "a" "b"
$row.names
integer(0)
$class
[1] "data.frame"
> attributes(df2)
$names
[1] "a" "b"
$class
[1] "data.frame"
Actually 'df2' is considered broken by validObject():
> validObject(df1)
[1] TRUE
> validObject(df2)
Error in validObject(df2) :
invalid class “data.frame” object: slots in class definition but
not in object: "row.names"
This is with R 2.15 and recent R devel.
Cheers,
H.
--
Hervé Pagès
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024
E-mail: hpa...@fhcrc.org
Phone: (206) 667-5791
Fax: (206) 667-1319
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