使用 Pandas groupby 从多行连接字符串 [英] Concatenate strings from several rows using Pandas groupby

问题描述

我想根据 Pandas 中的 groupedby 合并数据帧中的多个字符串.

I want to merge several strings in a dataframe based on a groupedby in Pandas.

这是我目前的代码:

import pandas as pd
from io import StringIO

data = StringIO("""
"name1","hej","2014-11-01"
"name1","du","2014-11-02"
"name1","aj","2014-12-01"
"name1","oj","2014-12-02"
"name2","fin","2014-11-01"
"name2","katt","2014-11-02"
"name2","mycket","2014-12-01"
"name2","lite","2014-12-01"
""")

# load string as stream into dataframe
df = pd.read_csv(data,header=0, names=["name","text","date"],parse_dates=[2])

# add column with month
df["month"] = df["date"].apply(lambda x: x.month)

我希望最终结果如下所示:

I want the end result to look like this:

我不知道如何使用 groupby 并在文本"列中应用某种字符串连接.任何帮助表示赞赏！

I don't get how I can use groupby and apply some sort of concatenation of the strings in the column "text". Any help appreciated!

推荐答案

您可以按 'name' 和 'month' 列分组，然后调用 transform 将返回与原始 df 对齐的数据，并在我们join 文本条目的地方应用 lambda:

You can groupby the 'name' and 'month' columns, then call transform which will return data aligned to the original df and apply a lambda where we join the text entries:

In [119]:

df['text'] = df[['name','text','month']].groupby(['name','month'])['text'].transform(lambda x: ','.join(x))
df[['name','text','month']].drop_duplicates()
Out[119]:
    name         text  month
0  name1       hej,du     11
2  name1        aj,oj     12
4  name2     fin,katt     11
6  name2  mycket,lite     12

我通过在此处传递感兴趣的列的列表 df[['name','text','month']] 来子原始 df，然后调用 drop_duplicates

I sub the original df by passing a list of the columns of interest df[['name','text','month']] here and then call drop_duplicates

EDIT 实际上我可以调用 apply 然后 reset_index :

EDIT actually I can just call apply and then reset_index:

In [124]:

df.groupby(['name','month'])['text'].apply(lambda x: ','.join(x)).reset_index()

Out[124]:
    name  month         text
0  name1     11       hej,du
1  name1     12        aj,oj
2  name2     11     fin,katt
3  name2     12  mycket,lite

更新

lambda 在这里是不必要的:

In[38]:
df.groupby(['name','month'])['text'].apply(','.join).reset_index()

Out[38]: 
    name  month         text
0  name1     11           du
1  name1     12        aj,oj
2  name2     11     fin,katt
3  name2     12  mycket,lite

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