Python Pandas: Is Order Preserved When Using groupby() and agg()?

Question

I\'ve frequented used pandas\' agg() function to run summary statistics on every column of a data.frame. For example, here\'s how you would produce the mean an

Answer 1

In order to preserve order, you'll need to pass .groupby(..., sort=False). In your case the grouping column is already sorted, so it does not make difference, but generally one must use the sort=False flag:

 df.groupby('A', sort=False).agg([np.mean, lambda x: x.iloc[1] ])