問題描述

我正在嘗試在 pandas 數(shù)據(jù)框中查找重復(fù)行.

I am trying to find duplicates rows in a pandas dataframe.

df=pd.DataFrame(data=[[1,2],[3,4],[1,2],[1,4],[1,2]],columns=['col1','col2'])

df
Out[15]: 
   col1  col2
0     1     2
1     3     4
2     1     2
3     1     4
4     1     2

duplicate_bool = df.duplicated(subset=['col1','col2'], keep='first')
duplicate = df.loc[duplicate_bool == True]

duplicate
Out[16]: 
   col1  col2
2     1     2
4     1     2

有沒有辦法添加引用第一個副本(保留的那個)的索引的列

Is there a way to add a column referring to the index of the first duplicate (the one kept)

duplicate
Out[16]: 
   col1  col2  index_original
2     1     2               0
4     1     2               0

注意:在我的情況下，df 可能非常大....

Note: df could be very very big in my case....

推薦答案

使用groupby，新建一列索引，然后調(diào)用duplicated:

Use groupby, create a new column of indexes, and then call duplicated:

df['index_original'] = df.groupby(['col1', 'col2']).col1.transform('idxmin')    
df[df.duplicated(subset=['col1','col2'], keep='first')]

   col1  col2  index_original
2     1     2               0
4     1     2               0

<小時>

詳情

我groupby前兩列然后調(diào)用transform + idxmin得到每個組的第一個索引.

I groupby first two columns and then call transform + idxmin to get the first index of each group.

df.groupby(['col1', 'col2']).col1.transform('idxmin') 

0    0
1    1
2    0
3    3
4    0
Name: col1, dtype: int64

duplicated 給了我想要保留的值的布爾掩碼:

duplicated gives me a boolean mask of values I want to keep:

df.duplicated(subset=['col1','col2'], keep='first')

0    False
1    False
2     True
3    False
4     True
dtype: bool

剩下的只是布爾索引.

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