R help - Oct 2002 - extracting variables with patttern templates

Hi all,
 I was wondering, does R have a facility to extract datasets based on a string
template. I know that you can do something like:
    X["a"]    # extract from 'X' the dataset named
'a'.

What I would like is something which says, from 'X' extract all the
datasets that have an 'a':
    X[pat = "a"]

I know that the 'pat' option can be used when just listing all the
object that exist, but is there any way to extract only certain
dataset from within an object using a smiliar technique.
Any help would be greatly appreciated.

Many Thanks!

Rishabh

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What is X?  The only things I can think of in R that could be thought to
contain datasets are lists, and they are extracted via [[ ]].
Or perhaps X is a data frame and you meant columns (`variables' but
perhaps also more general objects).

In either case you can do this by indexing.  To extract all the columns of
a data frame whose name contains `a' I can use

X[grep("a", names(X))]

and that allows regular expressions just like the `pattern' argument of
ls/objects.

It's hard to give precise answers to vague questions, but I hope that
gives
you enough of an idea.

On Tue, 22 Oct 2002, Rishabh Gupta wrote:
> Hi all,
>  I was wondering, does R have a facility to extract datasets based on a
string template. I know that you can do something like:
>     X["a"]    # extract from 'X' the dataset named
'a'.
>
> What I would like is something which says, from 'X' extract all the
datasets that have an 'a':
>     X[pat = "a"]
>
> I know that the 'pat' option can be used when just listing all the
object that exist, but is there any way to extract only certain
> dataset from within an object using a smiliar technique.
> Any help would be greatly appreciated.
>
> Many Thanks!
>
> Rishabh
>
>
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> r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
> Send "info", "help", or "[un]subscribe"
> (in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
>
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>
-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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