在Python DataFrames中查找？

Question

我有一個數據框df1：

Month

1
3
March
April
2
4
5

我有另一個數據框df2：

Month  Name

1       January
2       February
3       March
4       April
5       May

如果要用df2中的相應名稱替換df1的整數值，可以使用哪種查找功能？

我想以此作為我的df1：

    Month

January
March
March
April
February
May

Answer 1

replace它

df1.replace(dict(zip(df2.Month.astype(str),df2.Name)))
Out[76]: 
      Month
0   January
1     March
2     March
3     April
4  February
5     April
6       May

Answer 2

您可以使用pd.Series.map然后使用fillna 。 請注意將字符串映射為字符串，或者將數字映射為數字：

month_name = df2.set_index('Month')['Name']

df1['Month'] = pd.to_numeric(df1['Month'], errors='coerce').map(month_name)\
                 .fillna(df1['Month'])

print(df1)

      Month
0   January
1     March
2     March
3     April
4  February
5     April
6       May

您也可以使用pd.Series.replace ，但這通常效率不高 。

Answer 3

一種替代方法是將map與以下功能一起使用：

def repl(x, lookup=dict(zip(df2.Month.astype(str), df2.Name))):
    return lookup.get(x, x)

df['Month'] = df['Month'].map(repl)
print(df)

輸出量

      Month
0   January
1  February
2     March
3     April
4       May

Answer 4

將map與一系列序列配合使用，只需確保您的dtypes匹配：

mapper = df2.set_index(df2['Month'].astype(str))['Name']
df1['Month'].map(mapper).fillna(df1['Month'])

輸出：

0     January
1       March
2       March
3       April
4    February
5       April
6         May
Name: Month, dtype: object