python - 将一个数据集中的值替换为另一个数据集中的值的有效方法

Question

我有这个代码:

for index, row in df.iterrows():
  for index1, row1 in df1.iterrows():
    if df['budget'].iloc[index] == 0:
        if df['production_companies'].iloc[index] == df1['production_companies'].iloc[index1]
            and df['release_date'].iloc[index].year == df1['release_year'].iloc[index1] :
                df['budget'].iloc[index] = df1['mean'].iloc[index1]

它可以工作，但需要很长时间才能完成。我怎样才能让它运行得更快？ 我也尝试过:

df.where((df['budget'] != 0 and df['production_companies'] != df1['production_companies']
    and df['release_date'] != df1['release_year']),
        other = pd.replace(to_replace = df['budget'],
            value = df1['mean'],  inplace = True))

它应该更快，但它不起作用。我该如何实现这一目标？ 谢谢!

df 看起来像这样:

budget; production_companies;   release_date    ;title    
0;  Villealfa Filmproduction Oy ;10/21/1988;    Ariel    
0;  Villealfa Filmproduction Oy ;10/16/1986;    Shadows in Paradise   
4000000;    Miramax Films;  12/25/1995; Four Rooms   
0;  Universal Pictures; 10/15/1993; Judgment Night   
42000;  inLoops ;1/1/2006;  Life in Loops (A Megacities RMX)   
...          

和df1:

production_companies;   release_year;   mean;
Metro-Goldwyn-Mayer (MGM);  1998;   17500000    
Metro-Goldwyn-Mayer (MGM);  1999;   12500000   
Metro-Goldwyn-Mayer (MGM);  2000;   12000000   
Metro-Goldwyn-Mayer (MGM)   ;2001   ;43500000  
Metro-Goldwyn-Mayer (MGM);  2002    ;12000000  
Metro-Goldwyn-Mayer (MGM)   ;2003;  36000000  
Metro-Goldwyn-Mayer (MGM);  2004    ;27500000   
...   

如果年份和生产公司相同，我想将 df 中的值 0 替换为 df1 中的“平均值”值。

Answer 1

不要使用循环来执行此任务

pandas 的主要优点是矢量化功能。

矢量化计算的一种方法是对齐索引，然后使用 pd.DataFrame.index.map。要提取年份，您需要先转换为日期时间。

数据来自@ALollz。

# convert release_date to datetime and calculate year
df['release_date'] = pd.to_datetime(df['release_date'])
df['year'] = df['release_date'].dt.year

# create mapping from df1
s = df1.set_index(['production_companies', 'release_year'])['mean']

# use map on selected condition
mask = df['budget'] == 0
df.loc[mask, 'budget'] = df[mask].set_index(['production_company', 'year']).index.map(s.get)

print(df)

#      budget           production_company release_date title  year
# 0   1000000  Villealfa Filmproduction Oy   1988-10-21   AAA  1988
# 1       100  Villealfa Filmproduction Oy   1986-10-18   BBB  1986
# 2  30000000  Villealfa Filmproduction Oy   1955-12-25   CCC  1955
# 3      1000                Miramax Films   2006-01-01   DDD  2006
# 4   5000000                Miramax Films   2017-04-13   EEE  2017