python itertools groupby函数

作用：以key分桶（一般来说应用于hadoop后的reduce阶段），lines包含顺序向下key的所有行

groupby函数的两个参数：

1. the data to group—数据
2. the function to group it with.，操作数据的函数—key

测试脚本：

from itertools import groupby

things = [("animal", "bear"), ("animal", "duck"), ("plant", "cactus"), ("vehicle", "speed boat"), ("vehicle", "school bus")]

for key, group in groupby(things, lambda x: x[0]):
    for thing in group:
        print "A %s is a %s." % (thing[1], key)
    print " "

测试数据：

A bear is a animal.
A duck is a animal.

A cactus is a plant.

A speed boat is a vehicle.
A school bus is a vehicle.

测试脚本2–for标准输入：

import itertools
import sys

for key, lines in itertools.groupby(sys.stdin,key = lambda x : x.split(" ")[:2]):
    for line in lines:
        print line,
        print key
    print "\n"