[Haskell-cafe] Inecxact map?

[Holger Siegel]

Am 13.03.2012 um 09:15 schrieb Morten Olsen Lysgaard:

> I'm running a project where i want to generate a map of a rather large data collection. The map is if the form: Data.Map.Map String a
> I'd like to be able to do inexact lookups on the map. Firstly, ignore the difference between upper lower case, that's easy. But secondly, have a function:
> 
> search :: (Num b) => Data.Map.Map String a -> String -> b -> [a]
> 
> This function is like the normal lookup, but it takes an extra argument b. B is the allowed character error rate. That is the Levenstein distance divided on the length. It should return all the strings that has an error rate lower that b and in a ordered manner, best first.
> 
> Is it possible to design such a datastructure efficiently?
> Does there already exist something like this?
> If not, where would i begin to create this?

You could take a trie and extend the lookup functions so that it also returns inexact matches up to a given error rate. That should be quite easy, because the definition of Levenshtein distance is recursive as well as the trie's lookup function.