Python Pandas join aggregated tables

Question

I have a data frame with two columns: product_id and rating. I'm trying to join two tables. One obtained from

a = data.groupby('product_id').count()

The other one

b = data.groupby('product_id').mean()

I'd like to have a table that has on its columns the

product_id  count   mean

Answer 1

尝试：

data.groupby('product_id').agg(['mean', 'count'])