python - 用数据框中组的平均值替换列值

Question

我有一个 DataFrame 作为

Page    Line    y
1        2      3.2
1        2      6.1
1        3      7.1
2        4      8.5
2        4      9.1

我必须用组中的平均值替换 y 列。我可以使用此代码使用一列进行分组。

df['y'] = df['y'].groupby(df['Page'], group_keys=False).transform('mean') 

我正在尝试通过“Page”和“Line”分组来替换 y 的值。像这样，

Page    Line    y
1        2      4.65
1        2      4.65
1        3      7.1
2        4      8.8
2        4      8.8

我在此站点上搜索了很多答案，但找不到此应用程序。将 python3 与 Pandas 一起使用。

Answer 1

您需要列名列表，groupby参数 by:

by : mapping, function, label, or list of labels

Used to determine the groups for the groupby. If by is a function, it’s called on each value of the object’s index. If a dict or Series is passed, the Series or dict VALUES will be used to determine the groups (the Series’ values are first aligned; see .align() method). If an ndarray is passed, the values are used as-is determine the groups. A label or list of labels may be passed to group by the columns in self. Notice that a tuple is interpreted a (single) key.

df['y'] = df.groupby(['Page', 'Line'])['y'].transform('mean') 
print (df)
   Page  Line     y
0     1     2  4.65
1     1     2  4.65
2     1     3  7.10
3     2     4  8.80
4     2     4  8.80

你的解决方案应该改为这个语法糖 - pass Series in list:

df['y'] = df['y'].groupby([df['Page'], df['Line']]).transform('mean')