pandas groupby 在多列中连接字符串
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pandas groupby concatenate strings in multiple columns
提问by Blue Moon
I have this pandas data frame:
我有这个Pandas数据框：
df = DataFrame({'id':['a','b','b','b','c','c'], 'category':['z','z','x','y','y','y'], 'category2':['1','2','2','2','1','2']})
which looks like:
看起来像：
category category2 id
0 z 1 a
1 z 2 b
2 x 2 b
3 y 2 b
4 y 1 c
5 y 2 c
What i'd like to do is to groupby id and return the other two columns as a concatenation of unique strings.
我想要做的是 groupby id 并将其他两列作为唯一字符串的串联返回。
The outcome would look like:
结果将如下所示：
category category2 id
0 z 1 a
1 zxy 2 b
2 y 12 c
回答by unutbu
Use groupby/aggto aggregate the groups. For each group, apply setto find the unique strings, and ''.jointo concatenate the strings:
使用groupby/agg聚集的群体。对于每个组，申请set查找唯一字符串，并''.join连接字符串：
In [34]: df.groupby('id').agg(lambda x: ''.join(set(x)))
Out[34]:
category category2
id
a z 1
b yxz 2
c y 12
To move idfrom the index to a column of the resultant DataFrame, call reset_index:
要从id索引移动到结果 DataFrame 的列，请调用reset_index：
In [59]: df.groupby('id').agg(lambda x: ''.join(set(x))).reset_index()
Out[59]:
id category category2
0 a z 1
1 b yxz 2
2 c y 12
