As another thought for you, consider Levenshtein_distance. Also the Perl module, Levenshtein.pm.

I think you are just looking for what are called N1 errors, that means: one substitution, or one deletion or one addition. Life gets complicated if you working with a subset of N2 that allows transpositions, that would be for example, RATE and ARTE would match, but that counts as 2 errors. Note 2 errors could also be RATE vs XATB which is completely different. So Levenshtein == 2 can produce a lot of false "positives".

The last pattern matching code that I wrote, analyzed the input string, then generated a regex dynamically which was compiled and run against the candidate strings. A lot of "yeah, but's" with code like that and very specific to my particular application. Just a comment that something like that is possible in Perl (have Perl write a program (a REGEX), and then run it).

I think that the standard Levenshtein module will do most of what you want and I would start there. There are links to other "string compares" in the doc's at Levenshtein.pm. If somebody else has built the wheel that you need, I would use it. Some of these things have XS modules which will run much more quickly than native Perl.

Update: I thought that I should mention yet another approximate matcher agrep, agrep wiki. The algorithms are top notch and agrep is fast. In a lot of cases it will outperform standard grep for simple matches.

The caveat here is that I am unsure of the code status. I was using agrep for all of my grepping until I caught it missing a match! I spent several days reducing my dataset into a "smallest" reproduceable error report and talked with the mantainer. He verified the problem, but indicated the difficulty of a fix. That was about a decade ago and I'm not sure what happened (i.e. whether the "Marshall" fix got implemented or not?). If it didn't then very rarely agrep will miss a match that it should get, even when used like standard grep. With that caveat, agrep is pretty cool. Certainly the algorithms are.

In reply to Re: Comparing Lines within a Word List by Marshall
in thread Comparing Lines within a Word List by dominick_t

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