pandas中grouopby使用（一）

#-*- coding:utf-8 -*-import pandas as pdimport numpy as npdf=pd.DataFrame({'key1':['a','a','b','b','a'],'key2':['one','two','one','two','one'],                 'data1':np.random.randn(5),'data2':np.random.randn(5)})#按key1进行分组，并计算data1列的平均值。grouped1=df['data1'].groupby(df['key1']).mean()print grouped1#结果：key1#a    1.386036#b   -1.026542#按key1,key2进行分组，并计算data1列的平均值。grouped2=df['data1'].groupby([df['key1'],df['key2']]).mean()print grouped2#结果：#key1  key2#a     one     1.927353#      two     0.303403#b     one    -1.629209#      two    -0.423874#按key1进行分组，计算data1，data2的平均值print df.groupby('key1').mean()#结果： data1     data2#key1                    #a     1.386036 -0.617593#b    -1.026542  0.150912#按key1，key2进行分组，计算data1，data2的平均值print df.groupby(['key1','key2']).mean()#结果：#              data1     data2#key1 key2                    #a    one   1.927353 -1.127173#     two   0.303403  0.401567#b    one  -1.629209 -0.027238#     two  -0.423874  0.329062#求groupby的sizeprint df.groupby('key1').size()#结果：#key1#a    3#b    2