Question

I want to extract few pieces of data from a string using a single regular expression. I made a pattern which includes these pieces as subexpressions in parentheses. In perl-like environment, I would simply pass these subexpressions to variables by code like myvar1=$1; myvar2=$2;, etc. – but how to do this in R?
For the moment, the only way I found to access these occurrences is through regexec. It is not very convenient because regexec does not support perl syntax and for other reasons. This is what I have to do now:

getoccurence <- function(text,rex,n) { # rex is the result of regexec function
  occstart <- rex[[1]][n+1]
  occstop  <- occstart+attr(rex[[1]],'match.length')[n+1]-1
  occtext  <- substr(text,occstart[i],occstop)
  return(occtext)
}
mytext <- "junk text, 12.3456, -01.234, valuable text before comma, all the rest"
mypattern <- "([0-9]+\\.[0-9]+), (-?[0-9]+\\.[0-9]+), (.*),"
rez <- regexec(mypattern, mytext)
var1 <- getoccurence(mytext, rez, 1)  
var2 <- getoccurence(mytext, rez, 2)  
var3 <- getoccurence(mytext, rez, 3)  

Obviously, it is quite clumsy solution, there should be something much better. I would appreciate any advices.

Answer 1

Have you had a look at regmatches?

> regmatches(mytext, rez)
[[1]]
[1] "12.3456, -01.234, valuable text before comma," "12.3456"                                      
[3] "-01.234"                     "valuable text before comma"                   

> sapply(regmatches(mytext, rez), function(x) x[4])
[1] "valuable text before comma"