Is 1 large Regex faster than 3 smaller ones?

John Machin sjmachin at lexicon.net
Sun Jun 3 23:29:49 CEST 2007


On Jun 4, 4:52 am, erikcw <erikwickst... at gmail.com> wrote:
> Hi,
>
> I need to match 3 small strings in a small text file (about 200 words
> of text).
>
> Would it be faster to write 1 compiled regex that matches all 3
> substrings in one go, or to use 3 separate regular expressions to do
> the same job?
>

Taking your question literally: we have no idea how long it might take
you to write alternative versions of source code.

Guessing that you mean "Which would run faster?": both should run over
a 200-word text file in imperceptibly different time (unless of course
you make a mistake), and the time should be tiny compared to the time
required to open the file (again unless of course you make a mistake).

I'd suggest that as a learning exercise you do both, check the
accuracy of both (text e.g. matching only 2 out of 3, sought strings
in different orders, etc), and then and only then worry about the time
it takes.

HTH,
John




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