removing characters from a string

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch 
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Vivek Rao
Sent: Tuesday, April 12, 2005 7:55 AM
To: r-help at stat.math.ethz.ch
Subject: [R] removing characters from a string

Is there a simple way in R to remove all characters from a 
string other than those in a specified set? For example, I 
want to keep only the digits 0-9 in a string.

In general, I have found the string handling abilities of R a 
bit limited. (Of course it's great for stats in general). Is 
there a good reference on this? Or should R programmers dump 
their output to a text file and use something like Perl or 
Python for sophisticated text processing?

I am familiar with the basic functions such as nchar, 
substring, as.integer, print, cat, sprintf etc.