mongodb mapreduce can save emit into collection?

Question

I have a function map created, is this

var m = function() { 
  hashtags = {}
  for(var i in this.entities.hashtags) {
    hashtags[this.entities.hashtags[i].text] = 1
  };
  var valor = {numtweets: 1 ,  
    dic_hastag: hashtags};
    print("  value: " + tojson(valor));
  emit(this.place.country_code, valor)
};

I start from a collection called tweets, and the output of my map function should have a variable numtweets: 1 and av ariable hastags with the entire list of tweet hastats with a 1. example Nuwtweets: 1, hastags: "hast1": 1, "hast2": 2, "hast3": 1 1.- I can have the result saved in a collection, to prove that it works well instead of print 2.- If not if I have to do mapreduce, what should be the function reduces, why not do anything, and so when executing this, the output of the map function

Db.runCommand ({
                       MapReduce: "tweets",
                       Map: m,
                       Reduce: r,
                       Query: {"place.country_code": "AD"},
                       Out: {replace: "resultat5fi"}
                     });

Any suggestions, help, anything will be welcome.

Answer 1

I suggest you to see this .

This the way to debug map functions easily with mongodb.

1. first, create your map function as you did

2. Then define an emit function that will print (or insert into a collection)

Example of emit function that insert into a toto collection.

var emit = function(key, value) {
  db.toto.insert({key: key, value: value});
}

3. Invoke a find function and apply your map function on each record

Example :

var myCursor = db.tweets.find( {} );

while (myCursor.hasNext()) {
    var doc = myCursor.next();
    map.apply(doc);
    print();
}

4. Then look at yout toto collection

This way :

db.toto.find()