[Rd] read.table() with quoted integers
dwinsemius at comcast.net
Tue Oct 1 18:29:07 CEST 2013
On Sep 30, 2013, at 6:38 AM, Joshua Ulrich wrote:
> On Mon, Sep 30, 2013 at 7:33 AM, Milan Bouchet-Valat <nalimilan at club.fr> wrote:
>> It seems that read.table() in R 3.0.1 (Linux 64-bit) does not consider
>> quoted integers as an acceptable value for columns for which
>> colClasses="integer". But when colClasses is omitted, these columns are
>> read as integer anyway.
>> For example, let's consider a file named file.dat, containing:
>>> read.table("file.dat", colClasses="integer")
>> Error in scan(file, what, nmax, sep, dec, quote, skip, nlines, na.strings, :
>> scan() expected 'an integer' and got '"1"'
>> 'data.frame': 2 obs. of 1 variable:
>> $ V1: int 1 2
>> The latter result is indeed documented in ?read.table:
>> Unless ‘colClasses’ is specified, all columns are read as
>> character columns and then converted using ‘type.convert’ to
>> logical, integer, numeric, complex or (depending on ‘as.is’)
>> factor as appropriate. Quotes are (by default) interpreted in all
>> fields, so a column of values like ‘"42"’ will result in an
>> integer column.
>> Should the former behavior be considered a bug?
> No. If you tell read.table the column is integer and it's actually
> character on disk, it should be an error.
My reading of the `read.table` help page is that one should expect that when there is an 'integer'-class and an `as.integer` function and "integer" is the argument to colClasses, that `as.integer` will be applied to the values in the column. Should I be reading elsewhere?
>> This creates problems when combined with read.table.ffdf from package
>> ff, since this function tries to guess the column classes by reading the
>> first rows of the file, and then passes colClasses to read.table to read
>> the remaining rows by chunks. A column of quoted integers is correctly
>> detected as integer in the first read, but read.table() fails in
>> subsequent reads.
> This sounds like a issue with read.table.ffdf. The column of quoted
> integers is *incorrectly* detected as integer because they're actually
> character on disk. read.table.ffdf should rely on how the data are
> actually stored on disk (via as.is=TRUE), not how read.table might
> convert them once they're read into R.
>> R-devel at r-project.org mailing list
> Joshua Ulrich | about.me/joshuaulrich
> FOSS Trading | www.fosstrading.com
> R-devel at r-project.org mailing list
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