Remember the MongoDB map&reduce get started operation

• Requirements Description

Use Map&reduce to calculate the number of students in each class between 10 and 20 years of age in several classes:

• Demand analysis
• Fields for student tables:

Db.students.insert ({classid:1, age:14, Name: ' Tom '})

Will classid Random 1 and 2, age between 8-25 years old randomly, name is randomly between 3-7 characters.

• Data Write
• Data written to Java script

Students write 10 million data to the Mrtask library:

 Package org.test; Import Java.util.arraylist;import java.util.list;import Java.util.random;import Com.mongodb.basicdbobject;import Com.mongodb.db;import Com.mongodb.dbcollection;import Com.mongodb.dbcursor;import Com.mongodb.DBObject;import Com.mongodb.mongoclient;import com.mongodb.ServerAddress; public class Testmongodbreplset {public static void main (string[] args) {try {List<serveraddre            ss> addresses = new arraylist<serveraddress> ();            ServerAddress Address1 = new ServerAddress ("172.16.16.89", 27017);            Addresses.add (ADDRESS1);            Mongoclient client = new Mongoclient (addresses);            DB db = Client.getdb ("Mrtask");             Dbcollection coll = db.getcollection ("Students");            Data is written to basicdbobject object = new Basicdbobject ();                for (int i = 1; I <= 10000000; i++) {object.append ("ClassID", 1 + (int) (Math.random () * 2)); Object.append ("Age", 8 + (int) (Math.random () * 17));                Object.append ("Name", GetName ());                Coll.insert (object);            Object.clear ();        }} catch (Exception e) {e.printstacktrace ();        }} public static String GetName () {ArrayList list = new ArrayList ();        for (char c = ' a '; c <= ' z '; C + +) {List.add (c);        } String str = "";        int end = 3 + (int) (Math.random () * 4);            for (int i = 0; i < end; i++) {int num = (int) (Math.random () * 26);        str = str + list.get (num);    } return str; } }

　　

• Viewing data writes

After viewing, there are 10 million data in the students table in the Mrtask library:

[Email protected] bin]#./mongo

MongoDB Shell version:2.6.11

Connecting To:test

> Show DBS

Admin (empty)

Local 0.078GB

Mrtask 3.952GB

Test 0.453GB

> Use Mrtask

Switched to DB Mrtask

> Db.students.find (). Count ()

10000000

• Map&reduce calculation
• Map calculation

> mapfun = function () {Emit (this.classid,1)}

• Reduce calculation

> reducefun=function (Key, values) {var count = 0; Values.foreach (function (v) {count + = V;}); return count;}

> FF = function (key, value) {return {classid:key, count:value};}

• Result output

> classid_res = Db.runcommand ({

MapReduce: "Students",

Map:mapfun,

Reduce:reducefun,

Out: "Students_classid_res",

FINALIZE:FF,

query:{age:{$GT: Ten, $lt: 20}}

});

• Calculation results

> Db.students_classid_res.find ()

{"_id": 1, "value": {"ClassID": 1, "Count": 2643128}}

{"_id": 2, "value": {"ClassID": 2, "Count": 2650870}}

Remember the MongoDB map&reduce get started operation