熊猫数据框中的平均值

Question

I have a dataframe, for example:

Val1    Val2
1        4
2        10
2        5
1        7
2        0
1        20

I want to get a mean of all numbers from Val2 that have Val1 value equal to 1 (in the same row). How can I do that without using loop?

Answer 1

你可以试试

df.groupby(['Val1'])['Val2'].mean()

Answer 2

I am supposing you just want the mean as a simple float number. In this case, you can do:

df[df["Val1"] == 1]["Val2"].mean()

Answer 3

其他答案也应该提供正确的答案，但是我认为最惯用的方法是： df.loc[df['Val1']==1, 'Val2'].mean()