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.

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"
}