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PERF: casting loc to labels dtype before searchsorted #14551

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Merged
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Nov 2, 2016
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PERF: casting loc to labels dtype before searchsorted #14551

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PERF: casting loc to labels dtype before searchsorted
jorisvandenbossche Nov 1, 2016
6447e4c
catch error if loc is a slice (partial indexing)
jorisvandenbossche Nov 1, 2016
700afa5
add whatsnew notice
jorisvandenbossche Nov 2, 2016
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1 change: 1 addition & 0 deletions pandas/indexes/multi.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1907,6 +1907,7 @@ def convert_indexer(start, stop, step, indexer=indexer, labels=labels):
return np.array(labels == loc, dtype=bool)
else:
# sorted, so can return slice object -> view
loc = labels.dtype.type(loc)
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maybe should do this like

loc, orig_loc = lables.dtype.type(loc), loc
if  loc != orig_loc:
    loc = orig_loc

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Yeah, I am not sure how much checking would be needed here.

My understanding is that it probably is not needed in this case, as loc is coming from loc = level_index.get_loc(key), and labels and level_index are from the same MultiIndex. So I would assume that get_loc can only return an existing label, and so should fit in the dtype of labels?

(but probably also not that a perf issue to do the check)

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that sounds right; if the test suite passes, prob ok!

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Apparently not :-)
But it's only a partial indexing test that fails. So loc could also be a slice, and it is expected in partial indexing that this raises an error in searchsorted, but now it raises already a slightly different error in dtype.type(loc). So that can easily be solved with:

                try:
                    loc = labels.dtype.type(loc)
                except TypeError:
                    # this occurs when loc is a slice (partial string indexing)
                    # but the TypeError raised by searchsorted in this case
                    # is catched in Index._has_valid_type()
                    pass

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sure, or just tests if its a scalar to begin with

i = labels.searchsorted(loc, side='left')
j = labels.searchsorted(loc, side='right')
return slice(i, j)
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