On Sep 15, 2010, at 6:10 PM, Magnus Thor Torfason wrote:
Hi all,
I ran into a small issue when converting a list of vectors to a data
frame. The Issue I'm having is described by the snippet below:
#########################################################
# Convert a list of vectors into a data.frame
strlen = 256
s.long.a = paste( letters[1+(0:strlen %% 26)], collapse="")
s.long.b = paste( letters[1+(strlen:0 %% 26)], collapse="")
v.long.a = rep(s.long.a, 2)
v.long.b = rep(s.long.b, 2)
# Convert when the list has no names for its elements
my.list = list(v.long.a, v.long.b)
my.df = as.data.frame(my.list)
# Here we get an error
my.df
I have also been annoyed at that behavior. I can make the problem go
away by shortening the assignment of names to nameless lists which
occurs about halfway through the code of the data.frame function:
.
.
else if (no.vn[[i]]) {
tmpname <- substr(deparse(object[[i]])[1L], 1, 10)
# the base data.frame fn does not use the substring shortening
if (substr(tmpname, 1L, 2L) == "I(") {
ntmpn <- nchar(tmpname, "c")
if (substr(tmpname, ntmpn, ntmpn) == ")")
tmpname <- substr(tmpname, 3L, max(ntmpn, 20) - 1L)
}
vnames[[i]] <- tmpname
.
.
No error and the names are c..abcdefg and c..wvutsrq.
Whether you want to muck with the code of data.frame, well, it's your
machine and if it breaks, the standard warranty applies, ..... you get
to keep both pieces.
--
David.
# This solves the problem
names(my.list) = c("a","b")
my.fixed.df = as.data.frame(my.list)
my.fixed.df
#########################################################
In short, the problem is that when there are no names attached to
the elements of the list, it creates very long names - if the
elements of the vectors themselves are long. And further, that names
that are in some since disallowed (can't be printed, for one), are
silently injected into a data.frame, leading to an error later on.
Better would be to error out in as.data.frame
Best would be if way of generating default names in this function
would be intelligent enough to never create names longer than - say
30 characters. Of course, explicit names should be honored.
Anyway, that's my thoughts on this issue. No patch attached, and I
will work around this, but at least it is out there now.
Best,
Magnus Thor
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and provide commented, minimal, self-contained, reproducible code.
