Meteor/Mongo Map/Reduce 2D Array

Question

I am learning Meteor/Javascript and have a issue I cant seem to figure out. This is more of a 2 part question.

Can I do what I am trying to do with Meteor Mongo and avoid mapping/reducing in Javascript?

How can I do a map/reduce of the 2D array mentioned below in Javascript? (would be a good learning example).

So here is the setup, I have a Mongo collection that has the following data;

{
  "_id" : "oBPoZCLo9JFhZGdtL",
  "guest" : "Jin",
  "itemLikes" : 25,
}
{
  "guest" : "Jin",
  "itemLikes" : 32,
  "_id" : "xz7AgJv52e8QF6XuA"
}
{
  "guest" : "Jin",
  "itemLikes" : 20,
  "_id" : "XHkJoJEDyxX8w9Zmc"
}
{
  "guest" : "Jin",
  "itemLikes" : 39,
  "_id" : "LeN5Nqhgdn79MCbct"
}
{
  "guest" : "Jim",
  "itemLikes" : 17,
  "_id" : "iuhM6v4yySrEpgeaY"
}
{
  "guest" : "Lex",
  "itemLikes" : 20,
  "_id" : "ed6dmDMzXKJRaBxFM"
}
{
  "guest" : "Lex",
  "itemLikes" : 35,
  "_id" : "dTiY7nEx9yNXQTp49"
}
{
  "guest" : "Mel",
  "itemLikes" : 21,
  "_id" : "XRb7Yz84nEDJhpSQh"
}
{
  "guest" : "Mel",
  "itemLikes" : 17,
  "_id" : "KX9TSsWrJREQtaSNu"
}
{
  "guest" : "Nance",
  "itemLikes" : 39,
  "_id" : "rJRr2WdBaWXEurbWf"
}

Here is the Meteor method call I am using to parse the data;

  myFunctionName: function () {
    var guestLikesTotal = []
    _.reduce(_.map(MyCollection.find().fetch(), function(doc) {
              //map
              return [doc.guest, doc.itemLikes];
              //the map gives me ["Jin", 25] for example
            }), 
            function(memo, num){ 
              //reduce
              if (guestLikesTotal.length == 0) {
                guestLikesTotal.push(num);
              } else {
                var count = guestLikesTotal.length;
                for(var i=0;i<count;i++) {
                  if(guestLikesTotal[i][0] == num[0]) {
                    guestLikesTotal[i][1] += num[1];
                  } else {
                      // not sure what to put here
                    }
                  }
                  // this is wrong because its pushing items with the same "name" into the array
                  guestLikesTotal.push(num);
                };
                return memo+=1;
              }, 0);
  return guestLikesTotal;
}

I am trying to get guestLikesTotal to look like this;

[["Jin",116],["Jim",17],["Lex",55],["Nance",56]]

Any help with the 2 questions would be greatly appreciated.

Answer 1

In javascript you could do this if your collection is in an array:

var arr2 = [];
data.reduce( function (a, current, index) {
  if (!arr2.hasOwnProperty(current.guest)) {
    arr2[current.guest] = 0;
  }
  arr2[current.guest] += current.itemLikes;
}, data[0]);

var desired_arr = [];
for(var i in arr2) {
  desired_arr.push([i, arr2[i]]);
}
console.log(desired_arr);

Full fiddle: http://jsfiddle.net/juvian/LDBsT/