两个数据帧中的条件替换

您必须在左侧使用df_1进行左连接,然后使用df_1中现有的目标列来填充连接产生的空值。

df_1 = pd.DataFrame()
df_2 = pd.DataFrame()

df_1['campaign'] = ['a', 'b', 'c', 'd']
df_1['goal'] =['order', 'order', 'off', 'order']

df_2['campaign'] = ['a', 'b', 'c']
df_2['goal'] = ['Subscription', 'order', 'Subscription']

# left join
df = df_1.merge(df_2.rename(columns={'goal': 'new_goal'}), on=['campaign'], how='left')
# replace nulls 
df['new_goal'].fillna(df['goal'], inplace=True)

df

+---+----------+-------+--------------+
|   | campaign | goal  |   new_goal   |
+---+----------+-------+--------------+
| 0 |    a     | order | Subscription |
| 1 |    b     | order |    order     |
| 2 |    c     |  off  | Subscription |
| 3 |    d     | order |    order     |
+---+----------+-------+--------------+

您可以选择所需的列,并根据需要重命名它们

df_final = df[['campaign', 'new_goal']].rename(columns={'new_goal': 'goal'})

这将覆盖df1中的值

import pandas as pd

df1 = pd.DataFrame({'campaign':['a','b','c','d'],'goal':['order','order','off','order',]})
df2 = pd.DataFrame({'campaign':['a','b','c','d'],'goal':['Subscription','order','Subscription','order',]})

df2.merge(df1, how= 'left')

>>  campaign    goal
    0   a   Subscription
    1   b   order
    2   c   Subscription
    3   d   order

你可以使用pandas。DataFrame.merge为此:

https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.merge.html

df1 = pd.DataFrame({'campaign': ['a','b','c','d'], 'goal': ['order','order','off','order']})
df2 = pd.DataFrame({'campaign': ['a','b','c'], 'goal': ['subscription','order','subscription']})

df_out=pd.merge(df2,df1,on='campaign',how='left',suffixes=('_df2','_df1'))

结果:

  campaign      goal_df2 goal_df1
0        a  subscription    order
1        b         order    order
2        c  subscription      off