hadoop学习-stream-Top K记录

求海量数据中最大的K个记录

来源于《hadoop实战》(hadoop in action)（美 拉姆）第4.7章节有关stream的习题。

数据源：apat63_99.txt 专利描述数据集，包含专利号、专利申请年份等等信息。可从美国国家经济研究局获得，网址为http://www.nber.org/patents

大约有290万条记录。

这里的脚本用的是python。

apat63_99.txt里面存有专利的各种信息，这里以第9列的专利特定专利声明个数作为排序的key值，将最大的K条完整记录输出。

apat63_99.txt格式：

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"PATENT","GYEAR","GDATE","APPYEAR","COUNTRY","POSTATE","ASSIGNEE","ASSCODE","CLAIMS","NCLASS","CAT","SUBCAT","CMADE","CRECEIVE","RATIOCIT","GENERAL","ORIGINAL","FWDAPLAG","BCKGTLAG","SELFCTUB","SELFCTLB","SECDUPBD","SECDLWBD"
3070801,1963,1096,,"BE","",,1,,269,6,69,,1,,0,,,,,,,
3070802,1963,1096,,"US","TX",,1,,2,6,63,,0,,,,,,,,,
3070803,1963,1096,,"US","IL",,1,,2,6,63,,9,,0.3704,,,,,,,
3070804,1963,1096,,"US","OH",,1,,2,6,63,,3,,0.6667,,,,,,,
3070805,1963,1096,,"US","CA",,1,,2,6,63,,1,,0,,,,,,,
3070806,1963,1096,,"US","PA",,1,,2,6,63,,0,,,,,,,,,
3070807,1963,1096,,"US","OH",,1,,623,3,39,,3,,0.4444,,,,,,,
3070808,1963,1096,,"US","IA",,1,,623,3,39,,4,,0.375,,,,,,,
3070809,1963,1096,,"US","AZ",,1,,4,6,65,,0,,,,,,,,,

Top_K.py:

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#!/usr/bin/env python
#encoding:utf-8

import sys

# Top_K
Top_K = int(sys.argv[1])

#源数据apat63_99.txt的第9列，表示特定专利声明个数
index=8

#初始化top_k数组,用来保存记录
top=[]
topresult=[]
for i in range(Top_K):
top.append(0)
topresult.append("")

#插入记录
def add(temp,record):
global index
global Top_K
global top
global topresult
i=0
if temp>top[0]:
top[0]=temp
topresult[0]=record
for i in range(Top_K-1):
if temp>top[i+1]:
top[i]=top[i+1]
topresult[i]=topresult[i+1]
else:
i=i-1
break

i=i+1
top[i]=temp
topresult[i]=record

for line in sys.stdin:
fields = line.strip().split(",")
if fields[index].isdigit():
val = int(fields[index])
add(val,line.strip())

#输出top_k记录
i=0
for i in range(Top_K-1,-1,-1):
print topresult[i]

对每条读入的记录，通过add函数判断并添加到topresult链表中。
add函数第一个参数temp，是用来排序的key值，这里传进去的也就是数据源中的第9列的值，即index=8

第二个参数是key值对应的完整专利描述记录。

在map阶段和reduce阶段都调用此脚本。即可完成Top K记录的查找。

运行指令：

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bin/hadoop jar contrib/streaming/hadoop-streaming-1.2.1.jar -input Top_K/apat63_99.txt -output output -mapper 'Top_K.py 8' -file Top_K.py -reducer 'Top_K.py 8' -file Top_K.py

参数中的8 表示希望求得最大的8条记录。

运行结果：

4533693,1985,9349,1983,"US","CA",538840,2,346,524,1,15,13,80,1,0.6444,0.6272,7.8875,6.7692,0.0909,0.0769,0.0127,0.0125

5812453,1998,14144,1994,"JP","",581270,3,348,365,2,24,22,0,1,,0.1694,,13.1818,0.1818,0.1818,,

4068298,1978,6584,1975,"US","OH",557440,2,393,707,2,22,12,24,1,0.7292,0.8194,12.7083,5.6667,0,0,0,0

4624109,1986,9825,1983,"US","CA",,1,394,60,4,45,3,2,1,0.5,0.4444,9,8.6667,,,,

4081478,1978,6661,1976,"US","MI",600480,2,472,564,1,14,7,1,0.8571,0,0.8333,4,9.5714,0.6,0.4286,1,1

4373527,1983,8446,1979,"US","MD",295920,2,642,604,3,32,6,49,1,0.414,0.4444,10.6939,6.8333,0,0,0.1087,0.102

4085139,1978,6682,1976,"US","MI",600480,2,706,564,1,14,7,1,0.8571,0,0.8333,14,9.5714,0.6,0.4286,0,0

5095054,1992,11757,1990,"DE","",618615,2,868,524,1,15,40,111,0.975,0.8442,0.8586,4.1622,14.45,0.0571,0.05,0.0093,0.009

参考资料：
http://blog.csdn.net/jtlyuan/article/details/7560905
《hadoop实战》(hadoop in action)（美 拉姆）