I'm a little surprised that 1 trillion comparisons is computationally infeasible.
Why? 1GHz is one billion cycles per second, so 1 trillion CPU instructions will take about 10 minutes. Given that a string comparison with multiple function calls will take at least hundreds or thousands of CPU cycles, this will take at least a day or so. Probably a lot more.

If you want to do fast, approximate comparison of strings, a lot of work has been done on that in bioinformatics. In particular, the popular BLAST and PSI-BLAST algorithms more or less solve this problem by creating an index of short substrings, then doing a full comparison where they match. You might try to develop something similar.

In reply to Re^2: Cluster a big bunch of strings by educated_foo
in thread Cluster a big bunch of strings by citromatik

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