pandas.Series.nunique
- 
Series.nunique(dropna=True)[source] - 
Return number of unique elements in the object.
Excludes NA values by default.
Parameters: - 
dropna : boolean, default True - 
Don’t include NaN in the count.
 
Returns: - 
nunique : int 
 - 
 
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Licensed under the 3-clause BSD License.
    https://pandas.pydata.org/pandas-docs/version/0.24.2/reference/api/pandas.Series.nunique.html