Pandas : remove SOME duplicate values based on conditions

问题

I have a dataset :

id    url     keep_if_dup
1     A.com   Yes
2     A.com   Yes
3     B.com   No
4     B.com   No
5     C.com   No

I want to remove duplicates, i.e. keep first occurence of "url" field, BUT keep duplicates if the field "keep_if_dup" is YES.

Expected output :

id    url     keep_if_dup
1     A.com   Yes
2     A.com   Yes
3     B.com   No
5     C.com   No

What I tried :

Dataframe=Dataframe.drop_duplicates(subset='url', keep='first')

which of course does not take into account "keep_if_dup" field. Output is :

id    url     keep_if_dup
1     A.com   Yes
3     B.com   No
5     C.com   No

回答1:

You can pass multiple boolean conditions to loc, the first keeps all rows where col 'keep_if_dup' == 'Yes', this is ored (using |) with the inverted boolean mask of whether col 'url' column is duplicated or not:

In [79]:
df.loc[(df['keep_if_dup'] =='Yes') | ~df['url'].duplicated()]

Out[79]:
   id    url keep_if_dup
0   1  A.com         Yes
1   2  A.com         Yes
2   3  B.com          No
4   5  C.com          No

to overwrite your df self-assign back:

df = df.loc[(df['keep_if_dup'] =='Yes') | ~df['url'].duplicated()]

breaking down the above shows the 2 boolean masks:

In [80]:
~df['url'].duplicated()

Out[80]:
0     True
1    False
2     True
3    False
4     True
Name: url, dtype: bool

In [81]:
df['keep_if_dup'] =='Yes'

Out[81]:
0     True
1     True
2    False
3    False
4    False
Name: keep_if_dup, dtype: bool

来源：https://stackoverflow.com/questions/38584061/pandas-remove-some-duplicate-values-based-on-conditions