Pandas unique函数

 

Pandas中Series对象的唯一值

unique()函数用于获取Series对象的唯一值。

唯一性按出现顺序返回。基于哈希表的唯一，因此不排序

以NumPy数组形式返回唯一值。如果是扩展数组支持的Series，则返回仅具有唯一值的该类型的新ExtensionArray

 

The unique() function is used to get unique values of Series object.

Uniques are returned in order of appearance. Hash table-based unique, therefore does NOT sort.

Syntax:

Series.unique(self)

Returns: ndarray or ExtensionArray
The unique values returned as a NumPy array. See Notes.

Notes: Returns the unique values as a NumPy array. In case of an extension-array backed Series, a new ExtensionArray of that type with just the unique values is returned. This includes

• Categorical
• Period
• Datetime with Timezone
• Interval
• Sparse
• IntegerNA

 

Examples

In [1]:

import numpy as np
import pandas as pd

In [2]:

pd.Series([2, 4, 3, 3], name='P').unique()

Out[2]:

array([2, 4, 3], dtype=int64)

In [3]:

pd.Series([pd.Timestamp('2019-01-01') for _ in range(3)]).unique()

Out[3]:

array(['2019-01-01T00:00:00.000000000'], dtype='datetime64[ns]')

In [4]:

pd.Series([pd.Timestamp('2019-01-01', tz='US/Eastern')
           for _ in range(3)]).unique()

Out[4]:

<DatetimeArray>
['2019-01-01 00:00:00-05:00']
Length: 1, dtype: datetime64[ns, US/Eastern]

 

An unordered Categorical will return categories in the order of appearance.

In [5]:

pd.Series(pd.Categorical(list('qppqr'))).unique()

Out[5]:

[q, p, r]
Categories (3, object): [q, p, r]

 

An ordered Categorical preserves the category ordering.

In [6]:

pd.Series(pd.Categorical(list('qppqr'), categories=list('pqr'),
                         ordered=True)).unique()

Out[6]:

[q, p, r]
Categories (3, object): [p < q < r]