[R] extracting variables with patttern templates

[ripley@stats.ox.ac.uk]

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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-- 
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)
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