frozenset的简单用法

使用frozenset，它们可以用作字典的键（普通集合不可以）。

# -*- coding: utf-8 -*-
"""
Created on Thu Mar 23 20:54:37 2017

@author: Rainey
"""
import pandas as pd

"""
user  sku
1  111
1  222
2  333
2  444
2  555
3  666
4  777
"""
df = pd.read_csv('11.csv')
favorable_reviews_by_users = dict((k, frozenset(v.values)) for k, v in df.groupby("user")["sku"])
print(len(favorable_reviews_by_users))
print(favorable_reviews_by_users)
"""
4
{1: frozenset({222, 111}), 2: frozenset({555, 444, 333}), 3: frozenset({666}), 4: frozenset({777})}
"""