pandas.Series.argsort
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Series.argsort(axis=0, kind='quicksort', order=None)[source]
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Overrides ndarray.argsort. Argsorts the value, omitting NA/null values, and places the result in the same locations as the non-NA values Parameters: axis : int (can only be zero) kind : {‘mergesort’, ‘quicksort’, ‘heapsort’}, default ‘quicksort’ Choice of sorting algorithm. See np.sort for more information. ‘mergesort’ is the only stable algorithm order : ignored Returns: argsorted : Series, with -1 indicated where nan values are present See also 
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Licensed under the 3-clause BSD License.
    https://pandas.pydata.org/pandas-docs/version/0.20.3/generated/pandas.Series.argsort.html