pandas 重复行去除，列值合并怎么做？

Question

city 列 chongqing 重复了，
但是population 列值比一样，
怎么可以做到合并一行，然后把population列两个不同的值存储到一个一列中？

Answer 1

df.astype(str).groupby(['year','city'], as_index=False).agg(list).eval("population = population.str.join(',')")

Answer 2

这样咩~

frame.groupby(['year', 'city'], sort=False)['population'].sum().reset_index()

   year       city  population
0  2016    Beijing        2100
1  2016   Shanghai        2300
2  2015  Guangzhou        1000
3  2017   Shenzhen         700
4  2016  Chongqing         300

Answer 3

import pandas as pd

data = {'year':[2012,2013,2014,2015,2015],
        'city':['A','A','B','C','C'],
        'pop':[1,2,3,4,5]}

frame = pd.DataFrame(data,columns=['year','city','pop'])
groups = frame["pop"].groupby([frame["year"],frame["city"]])

year = []
city = []
pop = []

for i in groups:
    print(i)
    year.append(i[0][0])
    city.append(i[0][1])
    temp = []
    for j in i[1].values:
        temp.append(j)
    pop.append(temp)
        
d = {'a':year,'b':city,'c':pop}
da = pd.DataFrame(d)

print(da)