peterzawistowicz

db.pairs.find( { _id.a: "u123", count: { $gt: 10 }} )
             .sort({ count: -1 })

peterzawistowicz

{ _id: { a: 2, b: 3 }, value: 36 }

peterzawistowicz

 var map = function() { 
	for (i = 0; i < this.items.length; i++) {
		for (j = i + 1; j <= this.items.length; j++) {
			emit({a: this.items[i] ,b: this.items[j] }, 1); // emit each item pair
		}
	}
}

 var reduce = function(key, values) 
                      { return Array.sum(values); } // Sum all occurrences of each item pair

peterzawistowicz

{ _id: "u123", items: [ 2, 3, 8 ] }

peterzawistowicz

 var map = function() { emit(userId, this.itemId); } // emit samples as userId: itemId
 var reduce = function(key, values) 
                      { return values; } // Return the array of itemIds the user has bought
 db.activities.mapReduce(map, reduce, 
  { query: { type: “ORDER”, time: { $gt: NOW-24H }}, // include only activities of type order int he last day
    out: { replace: "lastDayOrders", sharded: true }) // persist the output to a collection

peterzawistowicz

db.lastHourUniques.count()

peterzawistowicz

db.lastHourUniques.find({ userId: "u123" })

peterzawistowicz

 var map = function() { emit(this.userId, 1); } // emit samples by userId with value of 1
 var reduce = function(key, values) 
                      	{ return Array.sum(values); } // sum the total samples per user
 db.activities.mapreduce(map, reduce, 
  	  	{ query: { time: { $gt: NOW-1H } }, // time bound the query to the last hour
		      out: { replace: "lastHourUniques", sharded: true }) // persist the output to a collection

peterzawistowicz

 db.activities.aggregate(([
   { $match: { time: { $gt: NOW-1H } }}, 
   { $group: { _id: "$userId", count: {$sum: 1} } }],
   { allowDiskUse: 1 })

peterzawistowicz

db.activities.aggregate(([
   { $match: { itemId: "301671", ts: { $gt: DATE }}}, 
   { $group: { _id: "$type", count: { $sum: 1 }}}])