[R] + and - in RODBC : no longer considered factors
Prof Brian Ripley
ripley at stats.ox.ac.uk
Wed Apr 30 12:49:14 CEST 2008
It is nothing to do with RODBC, which follows read.table here:
% cat > foo.txt
> read.table("foo.txt", header=TRUE)
and that uses
> type.convert(c("+", "-"))
 0 0
> type.convert(c("+", "a"))
 + a
Levels: + a
Whereas 2.6.2 did
> type.convert(c("+", "-"))
 + -
Levels: + -
The difference is related to a change to deciding in R (and not the OS)
what a 'numeric field' is:
o Parsing and scanning of numerical constants is now done by R's
own C code. This ensures cross-platform consistency, and
mitigates the effects of setting LC_NUMERIC (within base R it
only applies to output -- packages may differ).
The format accepted is more general than before and includes
binary exponents in hexadecimal constants: see
?NumericConstants for details.
There's a comment in the sources that numeric fields with no digits should
perhaps be regarded as non-numeric, so this can easily be changed.
On Wed, 30 Apr 2008, Dieter Menne wrote:
> I have a large Sweave report that reads data from a database file. Some of
> the columns are 1-character strings containing only +, - or NA. An example
> for such a table is shown below, and can be downloaded for easier testing
> (For security reasons, the file is zipped)
> table test
> hp hp1
> + a
> - +
> channel = odbcConnectAccess("test.mdb")
> ret = sqlQuery(channel,"select * from test")
> # 'data.frame': 2 obs. of 2 variables:
> # $ hp : num 0 0
> # $ hp1: Factor w/ 2 levels "+","a": 2 1
> Note that the column hp with "+" and "-" only is read as numeric 0, but
> when there is only other character such as in hp1, the conversion occurs.
> In R 2.6.2 (or was it an earlier version of RODBC?), column hp was treated
> as factor.
> Is this a new feature I have to live with, or an ... ahem ... issue? I know
> that with as.is I can get around this, but it need a lot of explicit
> programming for the columns I don't want to be as.issed
> -- Yes, I know I should have reported this earlier, but the problem of
> to re-create the report came up today.
> -- Yes, I should have reported this on the windows/devel r-help or directly
> to the author (of RODBC; or base?), so I feel guilty in advance that this is
> the wrong list.
> -- Yes, I have read the NEWS, and could not find something related.
> -- Yes, I cannot rule out this is a user error.
> R version 2.7.0 (2008-04-22)
> attached base packages:
>  stats graphics grDevices utils datasets methods base
> other attached packages:
>  RODBC_1.2-3
> R-help at r-project.org mailing list
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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