BUG: use size attribute (not method call)
BUG: force float64 dtype in object results for groupby
BUG: unstack fails in PeriodIndex
Merge pull request #7089 from cpcloud/groupby-size-windows-bug

BUG: use size attribute (not method call)
Merge pull request #7041 from sinhrks/unstack

BUG: unstack fails in PeriodIndex
ENH/API: accept percentiles in describe

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