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Fix sample with `frac` argument on postrgres backend. #1452

merged 12 commits into from Mar 19, 2016


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kwmsmith commented Mar 18, 2016

Subsumes #1425 and #1424.

Closes #1423.

@kwmsmith kwmsmith added this to the 0.10 milestone Mar 18, 2016


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kwmsmith commented Mar 18, 2016


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sandhujasmine commented Mar 18, 2016

Looks good - it contains tests for various sample() configurations.

And sample(frac= is working correctly; however, saw small inconsistencies between using sample() for a pandas backend vs DB backend.

  1. When using sample(n=176) if the result set has 175 rows, for the DB backend we get all rows but pandas backend raises an error. The pandas sample works a little bit differently.
  2. Also, in an example, found that using frac=0.3 for DB returns 53 rows while pandas (read from CSV file) returns 52 rows; basically one is rounding down and the other is rounding (ceil) up.

Would be good to have consistent behavior if looking at same data either from files or loaded up in DB. This is more when testing the same symbolic (unbound) expression against different resources.

Maybe we should work towards merging this as is, then add failing tests to reproduce above cases, then work on solutions?

kwmsmith added a commit that referenced this pull request Mar 19, 2016

Merge pull request #1452 from kwmsmith/fix-sample-frac-postgres
Fix sample with `frac` argument on postrgres backend.

@kwmsmith kwmsmith merged commit 3c63208 into blaze:master Mar 19, 2016

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@kwmsmith kwmsmith deleted the kwmsmith:fix-sample-frac-postgres branch Mar 19, 2016

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