MapReduce 简单的全文搜索2

上一个全文搜索实现了模糊查找，这个主要实现了精确查找，就是比如你查找mapreduce is simple那么他就只查找有这个句子的文章，而不是查找有这三个单词的文章。

这个版本需要重写反向索引，因为需要查找句子，所以需要定位每个单词的在文章中的位置，所以我们的反向索引需要加上单词所在的位置，即我们希望的输出是：

MapReduce file1.txt:<1,2,3>;file2.txt:<5,3,1>;这种格式的。

其实这一步比较简单。我们在map的时候输出为

“filename+word” position这样的<key,value>

“file1.txt:MapReduce”1

经过本地的combiner将其输出为：

“filename” “word:<position>” 

"file1.txt" "MapReduce:<1,2,3>"

最后经过reduece将所有同一个文件的单词归一,输出为

"filename" "word1:<position>;word2:<position>...."

"file1.txt" "MapReduce:<1,2,3>;simple:<5,6,7>"这种格式的

PS：由于这里的读取是从文件中每次读取一行，所以这里的position只是每一行上的位置，为非该单词在全文中的位置，如果遇到一句话横跨两行，那么这个程序就无法识别了，好像需要重写那个Input了，等下一个版本再修改

 

接下来主要就是根据索引来查找

大致的思路就是

Map阶段通过需要查找的句子例如MapReduce is simple来筛选反向索引中的单词，最后经过Map后得到在被查找的句子中的单词。输出为：

"filename" "word<position>"

"file1.txt" "MapReduce<1,2,3>"

经过reduce，则会把所有相同的文件的word给放在一起。由于reduce中单词的顺序是混乱的，所以为了识别句子，我这里增加了一个类

class  Address implements Comparable<Address>{

                 public String word ;

                 public int index;

                Address(String word, int index){

                                 this.word =word;

                                 this.index =index;

                }

                 public String toString(){

                                 return word +" "+ index;

                }

                 public int compareTo(Address a){

                                 if(index <a.index) return -1;

                                 else return 1;

                }

}

 

主要的word是用于放单词，index用于放索引，通过将同一个file下的value拆分到Address中，并且按照index进行排序，那么我们就能获得例如

M 1

M 2

M 3

i    4

s   5

i    6

M   7

（M代表Mapreduce i代表is，s代表simple）

那么如何识别这里的句子呢，首先这里的index必须是相邻的，并且这相邻的单词的顺序必须是M i s。为了识别相邻的单词的顺序问题，我这里新建了一个list，用于放输入的参数，也就是我要查找的句子，

ArrayList<String> sentence= new ArrayList<String>();

                                 for (i=2;i<wordnum+2;i++){

                                                String arg=conf.get("args" +i);

                                                sentence.add(arg);

                                }

 

接下来我们建立两个游标，一个指向上一个 word position一个指向当前，如果说上一个的word和当前的word在sentence中的位置刚好是相邻的，并且两个index也是相邻的那么n++,接着这两个游标都往下一步走，继续判断，直到n等于句子中单词的长度，那就说明已经匹配到了一个完整的句子。接着n=1再继续往下走，直到遍历完

具体代码：

 

public class MyMapper extends Mapper<LongWritable, Text, Text, Text> {

 

                 public void map(LongWritable ikey, Text ivalue, Context context)

                                                 throws IOException, InterruptedException {

                                Configuration conf=context.getConfiguration();

                                ArrayList< String> contents=new ArrayList< String>();

                                 int agrsnum=Integer.parseInt(conf.get( "argsnum"));

                                 int i=0;

                                 for (i=2;i<agrsnum;i++){

                                                 String arg=conf.get("args"+i);

                                                contents.add(arg);

                                }

                                 String line=ivalue.toString();

                                 String key=line.split("         ")[0];

                                 String value=line.split("      ")[1];

                                 for(String content:contents){

                                                 if(content.compareTo(key)==0){

                                                                StringTokenizer st=new StringTokenizer(value,";" );

                                                                 while(st.hasMoreTokens()){

                                                                                 String s=st.nextToken();

                                                                                 String filename=s.split(":")[0];

                                                                                 String adds=s.split(":")[1];

                                                                                 String val=key+adds;

                                                                                 //System.out.println(filename+"  "+ val);

                                                                                

                                                                                 //System.out.println("                             ");

                                                                                context.write( new Text(filename),new Text(val));

                                                                }

                                                }

                                }

                }

 

}

 

 

 

class  Address implements Comparable<Address>{

                 public String word ;

                 public int index;

                Address(String word, int index){

                                 this.word =word;

                                 this.index =index;

                }

                 public String toString(){

                                 return word +" "+ index;

                }

                 public int compareTo(Address a){

                                 if(index <a.index) return -1;

                                 else return 1;

                }

}

 

public class MyReducer extends Reducer<Text, Text, Text, Text> {

 

                 public void reduce(Text _key, Iterable<Text> values, Context context)

                                                 throws IOException, InterruptedException {

                                 // process values

                                Configuration conf=context.getConfiguration();

                                 int wordnum=Integer.parseInt(conf.get( "argsnum"))-2;

                                 int i=0;

                                ArrayList<String> sentence= new ArrayList<String>();

                                 for (i=2;i<wordnum+2;i++){

                                                String arg=conf.get("args" +i);

                                                sentence.add(arg);

                                }

                                

                                ArrayList<Address> list= new ArrayList<Address>();

                                

                                 for (Text val : values) {

                                                String[] line=val.toString().split("<|>|," );

                                                 for(int j=1;j<line.length;j++){

                                                                Address a=new Address(line[0],Integer.parseInt(line[j]));

                                                                list.add(a);

                                                }

                                                i++;

                                }

                                Collections. sort(list);

                                

                                 for(Address x:list){

                                                System. out.println(x);

                                                System. out.println("                    " );

                                }

                                

                                 int sum=0;

                                 int n=1;

                                Address start=list.get(0);

                 for(i=0;i<list.size();i++){

                                Address now=list.get(i);

                                 if(sentence.indexOf(now.word )-sentence.indexOf(start.word)==1&&now. index-start.index ==1){

                                                n++;

                                                start. word=now.word ;

                                                start. index=now.index ;

                                } else{

                                                n=1;

                                                start. word=now.word ;

                                                start. index=now.index ;

                                }

 

                                                 if(n==wordnum){

                                                                System. out.println("match is " +now);

                                                                sum++;

                                                                n=1;

                                                }

                                                

                                

                }

                                

                                 /*

                                for (i=0;i<list.size()-2;i++){

                                Address t1=list.get(i);

                                Address t2=list.get(i+1);

                                Address t3=list.get(i+2);

                                if((t1.index+2)==t3.index&&(t2.index+1)==t3.index){

                                                if(t1.add!=t2.add&&t1.add!=t3.add&&t2.add!=t3.add){

                                                                sum++;

                                                }

                                }

                                

                }

                

                

                System.out.println("                                       ");

                System.out.println("sum is "+sum);

                System.out.println("                                       ");

                */

                                 if(sum>0){

                                                context.write(_key, new Text(String.valueOf(sum)));

                                }

                }

 

}