R help - Dec 2002 - Wish list: add an "until" or "EOF.marker" parameter to scan & rea dLines

A bit late for Santa, but on my wish-list nevertheless:

is there any chance that "scan" and "readLines" could be
extended to take a
parameter "until" or "EOF.marker", which would be a
character string that
(if encountered while reading) would cause the reading to stop, just as if
an end-of-file had been found? [But leaving a connection open, so that
subsequent calls could read the rest of the file.] Compatibility could be
ensured by making "until" default to as.character( NA), which can
never be
encountered. If the "until" string isn't encountered when reading,
then
reading continues until a real end-of-file (or the "n" parameter is
satisfied).

This would be useful in all sorts of contexts; one example is in processing
a single data file that's made up of multiple segments each of different
formats. 

cheers
Mark

*******************************

Mark Bravington
CSIRO (CMIS)
PO Box 1538
Castray Esplanade
Hobart
TAS 7001

phone (61) 3 6232 5118
fax (61) 3 6232 5012
Mark.Bravington at csiro.au

Why is this necessary?  There are plenty of ways to do this already via
connections, e.g copy line-by-line to an anonymous file connection and
then scan from that.

Yes, it is useful, and that's why people already supplied you with a more
general tool, namely connections.  Please do look at the internals of scan
before suggesting complicating it further: it is already close to
unmaintainable.

I don't think R-help is the place for wishlist items: there is R-devel and
the R-bugs list has a wishlist section too (but please note that this gets
little action due to the perceived usefulness of the wishes).

On Fri, 27 Dec 2002 Mark.Bravington at csiro.au wrote:
> A bit late for Santa, but on my wish-list nevertheless:
>
> is there any chance that "scan" and "readLines" could
be extended to take a
> parameter "until" or "EOF.marker", which would be a
character string that
> (if encountered while reading) would cause the reading to stop, just as if
> an end-of-file had been found? [But leaving a connection open, so that
> subsequent calls could read the rest of the file.] Compatibility could be
> ensured by making "until" default to as.character( NA), which can
never be
> encountered. If the "until" string isn't encountered when
reading, then
> reading continues until a real end-of-file (or the "n" parameter
is
> satisfied).
>
> This would be useful in all sorts of contexts; one example is in processing
> a single data file that's made up of multiple segments each of
different
> formats.
>
> cheers
> Mark
>
> *******************************
>
> Mark Bravington
> CSIRO (CMIS)
> PO Box 1538
> Castray Esplanade
> Hobart
> TAS 7001
>
> phone (61) 3 6232 5118
> fax (61) 3 6232 5012
> Mark.Bravington at csiro.au
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> http://www.stat.math.ethz.ch/mailman/listinfo/r-help
>
-- 
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