REF: Manager.fast_xs to return SingleBlockManager instead of array #47077
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jorisvandenbossche
added
the
Internals
| name=self.index[i], | ||
| dtype=new_values.dtype, | ||
| ).__finalize__(self) | ||
| copy = isinstance(new_mgr.array, np.ndarray) and new_mgr.array.base is None |
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not for this PR, but this line is something we should handle more systematically, will be wrong for NDArrayBackedEAs
yehoshuadimarsky
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Jul 13, 2022
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This is something that I encountered in #46958, but again something that can be broken off / potentially useful anyway.
Currently the
fast_xsmethod returns an array, but the only two places where it is being used (xs/_ixs), this array is directly wrapped in a Series. So by lettingfast_xsreturn a manager instead, this gives a slight simplification / faster series construction.The reason that it is also useful for #46958 is because the CoW is handled at the manager level, so when creating a subset of a DataFrame (here in
xs), ideally that is done by creating a subset manager (with proper references if needed) instead of going through raw arrays (as how it is done for example when accessing a column as a Series).