I don't care much for regmatches and haven't tried strextract, but I think
replacing the character(0) by NA_character_ is almost always inappropriate
if the match information comes from gregexpr.
I think strcapture() does a pretty good job of what I think you are trying
to do. Perhaps adding an argument to map no match to NA instead of ""
would give you just what you wanted.
> x <- c("Groucho <grou...@marx.com>", "<ch...@marx.com>", "Harpo")
> d <- strcapture("([[:alpha:]]+)?( *<([[:alpha:]. ]+@[[:alpha:]. ]+)>)?",
x, proto=data.frame(Name=character(), Junk=character(),
Address=character(), stringsAsFactors=FALSE))
> d[c("Name", "Address")]
Name Address
1 Groucho grou...@marx.com
2 ch...@marx.com
3 Harpo
> str(.Last.value)
'data.frame': 3 obs. of 2 variables:
$ Name : chr "Groucho" "" "Harpo"
$ Address: chr "grou...@marx.com" "ch...@marx.com" ""
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Thu, Aug 15, 2019 at 11:31 AM Cyclic Group Z_1 <cyclicgroup...@yahoo.com>
wrote:
> I do think keeping the default behavior is desirable for backwards
> compatibility; my suggestion is not to change default behavior but to add
> an optional argument that allows a different behavior. Although this can be
> implemented in a user-defined function, retaining empty matches facilitates
> programmatic use, and seems to be something that should be available in
> base R. It is available, for example, in MATLAB, a comparable array
> language.
>
> Alternatively, perhaps a nomatch (or maybe emptymatch) argument in the
> spirit of `[.data.table`? That is, an argument nomatch where nomatch = NULL
> (the default) results in drops for vector outputs and character(0) for list
> outputs and nomatch = NA results in insertion of NA_character_, and nomatch
> = '' results in insertion of empty string.
>
> I can submit proposed patch code if others think this is a good idea.
>
> What are your thoughts on the proposed alteration to (currently
> nonexported) strextract? I assume (maybe wrongly) that the plan is to
> eventually export that function.
>
> Thank you,
> CG
>
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