python - Pandas 按条件分组

Question

这是我的数据 -

FROM    TO  DIRECTION    AMOUNT  
B    A    IN    100
A    B    OUT    200
A    B    IN    300
B    A    OUT    40

作为输出，我想显示谁总共支付了谁的摘要 -

FROM    TO    AMOUNT
A    B    300
B    A    340

澄清一下，如果 A --> B 是第 2 行和第 1 行(IN 表示从 TO 传输到 FROM，OUT表示从FROM传输到TO)

我在使用 .groupby() 方式时遇到问题。我尝试过的 -

df.groupby(['FROM', 'TO', 'DIRECTION'])

但这当然似乎并不能解决问题。任何帮助表示赞赏。

Answer 1

Idea 是按条件交换 FROM 和 TO 的值:

mask = df['DIRECTION'] == 'IN'
df.loc[mask, ['TO', 'FROM']] = df.loc[mask, ['FROM', 'TO']].values
print (df)
  FROM TO DIRECTION  AMOUNT
0    A  B        IN     100
1    A  B       OUT     200
2    B  A        IN     300
3    B  A       OUT      40

然后聚合sum:

df = df.groupby(['FROM', 'TO'], as_index=False)['AMOUNT'].sum()
print (df)
  FROM TO  AMOUNT
0    A  B     300
1    B  A     340

如果不想修改原始DataFrame，则解决方案非常相似:

mask = df['DIRECTION'] == 'IN'
df1 = df[['TO','FROM']].mask(mask, df[['FROM','TO']].values)
#output is same like above, only changed order of columns
print (df1)
  TO FROM
0  B    A
1  B    A
2  A    B
3  A    B

df2 = df['AMOUNT'].groupby([df1['FROM'], df1['TO']]).sum().reset_index()
print (df2)
  FROM TO  AMOUNT
0    A  B     300
1    B  A     340