[Rd] Commas in formatC

[David Brahm]

formatC() is great for formatting numbers!  But it would be even better if it
could optionally insert commas (or semicolons), e.g.
 R> formatC(1234567.89, digits=2, format="f", commas=T)
    [1] "1,234,567.89"

Here's a snippet of code that does that, which could more or less just be
inserted into at the end of formatC if any R-core guru were so inclined.  "r"
is the result so far, and "commas" is a logical flag:

  stp <- regexpr("[0-9]+", r);  len <- attr(stp, "match.length")
  if (commas && (maxl <- max(len)) > 3) for (i in seq(3, maxl-1, 3))
    r[len>i] <- paste(substring(r[len>i], 1, (stp+len-1-i)[len>i]),
                      substring(r[len>i], (stp+len-i)[len>i]), sep=",")
-- 
                              -- David Brahm (brahm@alum.mit.edu)
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