R devel - Jul 2005 - R 2.1.1: read.table processes C-style escapes (PR#8037)

In R 2.1.1, the default behaviour of scan() was changed to process all 
C-style escapes, even when a delimiter was specified using the 'sep' 
argument. A new argument 'allowEscapes' was introduced to turn this 
processing off.

Because read.table() calls scan(), read.table() inherits the new default 
behaviour of scan() but without a way to turn it off. For example, reading 
a file testdata.txt' containing

X
A
\0
C

produces

 > read.delim("testdata.txt")
[1] X
<0 rows> (or 0-length row.names)

It seems that all the occurances of scan() within read.table() need to have 
'allowEscapes=FALSE' added to the argument string.

Gordon

 > version
          _
platform i386-pc-mingw32
arch     i386
os       mingw32
system   i386, mingw32
status   Patched
major    2
minor    1.1
year     2005
month    07
day      22
language R
---------------------------------------------------------------------------------------
Dr Gordon K Smyth, Senior Research Scientist, Bioinformatics,
Walter and Eliza Hall Institute of Medical Research,
1G Royal Parade, Parkville, Vic 3050, Australia
Tel: (03) 9345 2326, Fax (03) 9347 0852,
Email: smyth at wehi.edu.au, www: http://www.statsci.org

>To: r-bugs at biostat.ku.dk
>From: Gordon Smyth <smyth at wehi.edu.au>
>Subject: R 2.1.1: read.table processes C-style escapes
>Date: Wed, 27 Jul 2005 12:51:45 +1000
>
>In R 2.1.1, the default behaviour of scan() was changed to process all 
>C-style escapes, even when a delimiter was specified using the 'sep'
>argument. A new argument 'allowEscapes' was introduced to turn this 
>processing off.
>
>Because read.table() calls scan(), read.table() inherits the new default 
>behaviour of scan() but without a way to turn it off. For example, reading 
>a file testdata.txt' containing
>
>X
>A
>\0
>C
>
>produces
>
> > read.delim("testdata.txt")
>[1] X
><0 rows> (or 0-length row.names)
>
>It seems that all the occurances of scan() within read.table() need to 
>have 'allowEscapes=FALSE' added to the argument string.
Or, alternatively and perhaps better, scan() could regain some of its 
earlier behaviour, to process C-style escapes by default only when 'sep'
is
NULL or empty. It seems, to me at least, that C-style escape sequences make 
sense only in some sort of source code, and delimited text can't be source 
code.

Gordon
>Gordon
>
> > version
>          _
>platform i386-pc-mingw32
>arch     i386
>os       mingw32
>system   i386, mingw32
>status   Patched
>major    2
>minor    1.1
>year     2005
>month    07
>day      22
>language R

On Wed, 27 Jul 2005, Gordon Smyth wrote:
> Thanks for the reply. Apologies for checking only R patched rather than 
> R-devel.
>
> I guess that this means that someone must have a use for allowEscapes=TRUE 
> when read reading a file in table format into a data frame. It is hard to 
> imagine.
Octal and hex escapes are a common way to cope with different encodings.

I would not want R limited by the imagination of a single user, let alone 
a Windows-only user.

-- 
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