pandas 去重函数 drop_duplicates() 和 选取重复行函数 duplicated()

1  drop_duplicates()  返回删除重复行后的DataFrame，可以仅选择某些列。索引、时间型索引都是被忽略。

pandas.DataFrame.drop_duplicates 官方文档

方法：

DataFrame.drop_duplicates(self, subset=None, keep='first', inplace=False)

参数：

subset : column label or sequence of labels, optional   子集： 列标签或标签序列，可选

Only consider certain columns for identifying duplicates, by default use all of the columns

只考虑标识重复项的某些列，默认情况下使用所有列

keep : {‘first’, ‘last’, False}, default ‘first’

• first : Drop duplicates except for the first occurrence. 删除重复行，只剩下第一次出现的重复行。
• last : Drop duplicates except for the last occurrence. 删除重复行，只剩下最后一次出现的重复行。
• False : Drop all duplicates. 删除全部重复行。

inplace : boolean, default False  默认为返回一个副本

Whether to drop duplicates in place or to return a copy

是直接在原数据上修改，还是返回一个副本

 举例：

1.1 创建DataFrame 

import pandas as pd  

data = pd.DataFrame({'Age': [37, 54, 38, 24, 54, 33, 54, 54, 18],
                     'Gender': ['Male', 'Female', 'Male', 'Male', 'Female', 'Male', 'Male', 'Female', 'Female'],
                     'MaritalStatus': ['Divorced', 'Single', 'Married', 'Married', 'Single', 'Married','Divorced', 'Single', 'Single']})

原始数据输出，第1，4，7行为重复行：

   Age  Gender MaritalStatus
0   37    Male      Divorced
1   54  Female        Single
2   38    Male       Married
3   24    Male       Married
4   54  Female        Single
5   33    Male       Married
6   54    Male      Divorced
7   54  Female        Single
8   18  Female        Single

1.2   keep='first' ，删除重复行，只剩下第一次出现的重复行

data_first = data.drop_duplicates(keep='first')
print(data_first)

删除了第4，7行的重复行，保留第1行的重复行，输出结果：

   Age  Gender MaritalStatus
0   37    Male      Divorced
1   54  Female        Single
2   38    Male       Married
3   24    Male       Married
5   33    Male       Married
6   54    Male      Divorced
8   18  Female        Single

1.3   keep='last' ，删除重复行，只剩下最后一次出现的重复行

data_last = data.drop_duplicates(keep='last')
print(data_last)

删除了第1，4行的重复行，保留第7行的重复行，输出结果：

   Age  Gender MaritalStatus
0   37    Male      Divorced
2   38    Male       Married
3   24    Male       Married
5   33    Male       Married
6   54    Male      Divorced
7   54  Female        Single
8   18  Female        Single

1.4   keep=False ，删除所有重复行

data_false = data.drop_duplicates(keep=False)
print(data_false)

删除了第1，4，7行的所有重复行，输出结果：

   Age  Gender MaritalStatus
0   37    Male      Divorced
2   38    Male       Married
3   24    Male       Married
5   33    Male       Married
6   54    Male      Divorced
8   18  Female        Single

1.5  默认inplace=False，返回一个副本

data.drop_duplicates(inplace=False， keep='last')

返回的为原数据副本，未改动，输出结果：

   Age  Gender MaritalStatus
0   37    Male      Divorced
1   54  Female        Single
2   38    Male       Married
3   24    Male       Married
4   54  Female        Single
5   33    Male       Married
6   54    Male      Divorced
7   54  Female        Single
8   18  Female        Single

1.6 inplace=True，直接在原数据上修改

data.drop_duplicates(inplace=True，keep='last')

删除了第1，4行的重复行，保留第7行的重复行，输出结果：

   Age  Gender MaritalStatus
0   37    Male      Divorced
1   54  Female        Single
2   38    Male       Married
3   24    Male       Married
5   33    Male       Married
6   54    Male      Divorced
8   18  Female        Single

2. duplicated() ，返回指示重复行的布尔级数(False 或 True)，可选地只考虑某些列。

pandas.DataFrame.duplicated 官方文档

方法：

DataFrame.duplicated(self, subset=None, keep='first')

参数：

subset : column label or sequence of labels, optional   子集： 列标签或标签序列，可选

Only consider certain columns for identifying duplicates, by default use all of the columns

只考虑标识重复项的某些列，默认情况下使用所有列

keep : {‘first’, ‘last’, False}, default ‘first’

• first : Mark duplicates as True except for the first occurrence. 将重复项标记为True(第一次出现的除外)。
• last : Mark duplicates as True except for the last occurrence. 将重复项标记为True(最后一次出现的除外)。
• False : Mark all duplicates as True. 将所有重复项标记为True。

举例：

2.1 创建DataFrame 

import pandas as pd  

data = pd.DataFrame({'Age': [37, 54, 38, 24, 54, 33, 54, 54, 18],
                     'Gender': ['Male', 'Female', 'Male', 'Male', 'Female', 'Male', 'Male', 'Female', 'Female'],
                     'MaritalStatus': ['Divorced', 'Single', 'Married', 'Married', 'Single', 'Married','Divorced', 'Single', 'Single']})

原始数据输出，第1，4，7行为重复行：

   Age  Gender MaritalStatus
0   37    Male      Divorced
1   54  Female        Single
2   38    Male       Married
3   24    Male       Married
4   54  Female        Single
5   33    Male       Married
6   54    Male      Divorced
7   54  Female        Single
8   18  Female        Single

2.2   keep='first' ，将重复项标记为True(第一次出现的除外)

data_first = data.duplicated(keep='first')
print(data_first)

标记重复行第4，7行为True，第1行重复行为False，输出结果：

0    False
1    False
2    False
3    False
4     True
5    False
6    False
7     True
8    False
dtype: bool

2.3  keep='last' ，将重复项标记为True(最后一次出现的除外)

data_last = data.duplicated(keep='last')
print(data_last)

标记重复行第1，4行为True，第7行重复行为False，输出结果：

0    False
1     True
2    False
3    False
4     True
5    False
6    False
7    False
8    False
dtype: bool

2.4  keep=False ， 将所有重复项标记为True。

data_false =data.duplicated(keep=False)
print(data_false)

标记重复行第1，4，7行为True，输出结果：

0    False
1     True
2    False
3    False
4     True
5    False
6    False
7     True
8    False
dtype: bool

选出重复行：
 

duplicated_rows = data_false[data_false==True]
print(duplicated_rows)

第1，4，7行为重复行，输出结果：

1    True
4    True
7    True