Implement Mapreduce with suitable example using MongoDB.
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The document implements a MapReduce operation using MongoDB to count the number of posts by each user with status "active" stored in a collection called c1. Four documents were inserted into the c1 collection. A MapReduce operation was run with a mapping function to emit each user_name with a count of 1, and a reducing function to sum the counts. The results of the operation were stored in a collection called "post_total". The find operation then displays the four documents inserted into the original c1 collection.
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Implement Mapreduce with suitable example using MongoDB.
- 1. Practical No:12 Problem Statement: Implement Mapreduce with suitable example using MongoDB. > use prac12 switched to db prac12 > db.c1.insert({"post_text": "India is an awesome country","user_name": ... "sachin", "status":"active"}) WriteResult({ "nInserted" : 1 }) > db.c1.insert({"post_text": "welcome to India","user_name": "saurav","status":"active"}) WriteResult({ "nInserted" : 1 }) > db.c1.insert({"post_text": "I live in India","user_name": "yuvraj","status":"active"}) WriteResult({ "nInserted" : 1 }) > db.c1.insert({"post_text": "India is great","user_name": "gautam","status":"active"}) WriteResult({ "nInserted" : 1 }) > db.c1.mapReduce( ... function() { emit(this.user_name,1); }, ... function(key, values) {return Array.sum(values)}, { ... query:{status:"active"}, ... out:"post_total" ... } ... ) { "result" : "post_total", "timeMillis" : 59, "counts" : { "input" : 4, "emit" : 4, "reduce" : 0, "output" : 4 }, "ok" : 1 } > ) > db.c1.find().pretty(); { "_id" : ObjectId("5d96eebda693e3d886aed428"), "post_text" : "India is an awesome country", "user_name" : "sachin", "status" : "active" } { "_id" : ObjectId("5d96eedfa693e3d886aed429"), "post_text" : "welcome to India", "user_name" : "saurav", "status" : "active" } { "_id" : ObjectId("5d96eef3a693e3d886aed42a"), "post_text" : "I live in India", "user_name" : "yuvraj", "status" : "active" } { "_id" : ObjectId("5d96ef08a693e3d886aed42b"), "post_text" : "India is great",
- 2. "user_name" : "gautam", "status" : "active" }