计算组的扩展标准差

Question

I would like to calculate the expanding standard deviation of aa group. I've tried the following:

df['RunStdDev']  =  df.groupby(['LEFT PORT DATE TIME'])['SPEED'].apply.pd.expanding_std()

I get error:

AttributeError: module 'pandas' has no attribute 'expanding_std'

What am I doing wrong?

Answer 1

It should be working

df['RunStdDev']  =  df.groupby['LEFT PORT DATE TIME']['SPEED'].apply.expanding_std()

You do not have to use .pd after apply function as df is an actuall pandas object with its methods imported.

Answer 2

Are you running latest pandas version?

df['RunStdDev']  =  df.groupby(['LEFT PORT DATE TIME'])['SPEED'].expanding().std()

pandas docs

Expanding.std(self, ddof=1, *args, **kwargs)