2021-03-31 使用pandas更新DataFrame某一列（值位于另一个DataFrame）

情景应用：按指定顺序班级进行各班参考人数统计

表1：存放考试安排表；表2：存放指定顺序的所有班级

目的：自动计算表2中指定顺序的所有班级参考人数

import pandas as pd

df1=pd.DataFrame({'id':[429,429,432,431,429,432,431,430,431,432],'name':['Andy1','Jacky1','Bruce1','rose','Andy1','Jacky1','Bruce1','rose','Andy1','Jacky1'],'target':[1,0,1,0,1,0,1,0,1,1]})
df2=pd.DataFrame({'id':[429,430,432],'name':['Andy2','Jacky2','rose2']})

B_song = df1.groupby(['id','target'])['target'].agg('count').rename().reset_index() 
print('\n',B_song)
#print('\n',B_song.columns)
B_song.rename(columns={0:'counts'},inplace=True)#更改列名

B_song=B_song[B_song['target']==1]
print('\n',B_song)

s = B_song.set_index('id')['counts']
#df1=pd.DataFrame(s).reset_index()
#df1=df1.set_index('id')
print('\n',s)

df2=df2.set_index('id')
df2['counts']= None
df2['counts'].update(s)

print('\n',df2)

代码结果：

PS D:\pcharm> & C:/Users/jiaoshi01/AppData/Local/Programs/Python/Python36-32/python.exe d:/pcharm/test002.py

 id  target  0

0 429 0 1
1 429 1 2
2 430 0 1
3 431 0 1
4 431 1 2
5 432 0 1
6 432 1 2

 id  target  counts

1 429 1 2
4 431 1 2
6 432 1 2

id
429 2
431 2
432 2
Name: counts, dtype: int64

    name counts

id
429 Andy2 2
430 Jacky2 None
432 rose2 2
PS D:\pcharm>