grouping strings by similarity

Programmer Question

I have an array of strings, not many (maybe a few hundreds) but often long (a few hundred chars).

Those string are, generally, nonsense and different one from the other.. but in a group of those string, maybe 5 out of 300, there's a great similarity. In fact they are the same string, what differs is formatting, punctuation and a few words..

How can I work out that group of string?

By the way, I'm writing in ruby, but if nothing else an algorithm in pseudocode would be fine.

thanks

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