原始數據如下：

u1 a,d,b,c u2 a,a,c u3 b,d u4 a,d,c u5 a,b,c
計算公式使用：sim = U(i)∩U(j) / (U(i)∪U(j))

其中：?(U(i)∪U(j)) =?U(i) + U(j) - ?U(i)∩U(j)?

原始的Hadoop實現需要5輪MR，優化后只需要兩輪就可以完成。

之前的輪數過多，主要在于計算(U(i)∪U(j)) 的時候，需要多次更改key，并非計算量大。只需要修改一下傳遞的key，就可以兩輪實現。

mapper_1.py

#!/usr/bin/python #-*-coding:utf-8-*- import sysfor line in sys.stdin:user,item_str = line.strip().split()item_list = sorted(list(set(item_str.split(','))))print "item_str:",item_str,"item_list:",item_listfor i in range(len(item_list)):i1 = item_list[i]print i1,1,'norm'for i2 in item_list[i+1:]:print i1,i2,1,'dot'
reducer_1.py

#!/usr/bin/python #-*-coding:utf-8-*- import sysdef PrintOut():i1 = old_keyprint i1,old_dict['norm'],'norm'for i2 in old_dict['dot']:print i1 + "-" + i2,old_dict['dot'][i2],old_dict['norm'],'dot-norm_i1'old_key = "" old_dict = {'norm':0,'dot':{}} for line in sys.stdin:sp = line.strip().split()if sp[-1] == 'norm':key,value = sp[:2]if key == old_key:old_dict['norm'] += int(value) else:if old_key != "":PrintOut()old_key = key# Notice: norm part should be int(value)old_dict = {'norm':int(value),'dot':{}}elif sp[-1] == 'dot':key,i2,value = sp[:3]if key == old_key:if i2 not in old_dict['dot']:old_dict['dot'][i2] = 0old_dict['dot'][i2] += int(value)else:if old_dot_key != "":PrintOut()old_key = keyold_dict = {'norm':int(value),'dot':{}}if old_key != "":PrintOut()
mapper_2.py

#!/usr/bin/python #-*-coding:utf-8-*- import sysfor line in sys.stdin:sp = line.strip().split()if sp[-1] == 'norm':print line.strip()elif sp[-1] == "dot-norm_i1":key,dot,norm_i1 = sp[:3]i1,i2 = key.split('-')print i2,i1,dot,norm_i1,'dot-norm_i1'
reducer_2.py

#!/usr/bin/python #-*-coding:utf-8-*- import sysdef GenSim(norm_i1,norm_i2,dot):return float(dot) / (int(norm_i1) + int(norm_i2) - int(dot))def PrintOut():i2 = old_keynorm_i2 = old_dict['norm']for i1 in old_dict['dot']:dot,norm_i1 = old_dict['dot'][i1]sim = GenSim(norm_i1,norm_i2,dot)print i1+"-"+i2,dot,norm_i1,norm_i2,sim,'dot,norm_i1,norm_i2,sim'old_key = "" old_dict = {'norm':"",'dot':{}} for line in sys.stdin:sp = line.strip().split()if sp[-1] == 'norm':key,value = sp[:2]if key == old_key:old_dict['norm'] = valueelse:if old_key != "":PrintOut()old_key = keyold_dict = {'norm':value,"dot":{}}elif sp[-1] == 'dot-norm_i1':key,i1,dot,norm_i1 = sp[:4] #key is i2.if key == old_key:if i1 not in old_dict['dot']:old_dict['dot'][i1] = (dot,norm_i1)else:if old_key != "":PrintOut()old_key = keyold_dict = {'norm':value,'dot':{i1:(dot,norm_i1)}}if old_key != "":PrintOut()
執行腳本 t.sh：

#!/bin/bashcat user_log.txt |./mapper_1.py |sort -k1 > d.m.1 cat d.m.1 |./reducer_1.py > d.r.1cat d.r.1 |./mapper_2.py |sort -k1 > d.m.2 cat d.m.2 |./reducer_2.py > d.r.2

總結

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