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Recode pool on overflow #892

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gustafsson
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groupby and join fails when joining multiple columns with many unique values each.

The possible number of permutations quickly grows higher than the actual number of realised permutations. This PR detects when this is about to happen and recodes the pool of realised unique values.

@gustafsson gustafsson mentioned this pull request Nov 22, 2015
@alyst
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alyst commented Nov 23, 2015

Actually I've tried similar approach before, but as for complex joins/groupbys you would call PooledDataArray(x) several times, and that implicitly builds a hash, it's faster to build the hash from the very beginning. This is implemented in #850. I use it on daily basis.

@gustafsson
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@alyst great catch, thanks. #850 looks much better. It passes the tests added in this PR so I'm in favour of using it instead of this PR.

@gustafsson gustafsson closed this Nov 23, 2015
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2 participants