Grouping and aggregation

In the following example we will perform grouping and aggregation in order to get statistics (sum, max, min, and avg) about NBA players and their number of points scored. First, the map function will send the name of the player and the number of points scored for each game. The map function will look similar to the following code:

function(){emit(this.player, this.points); }

Then, we can perform all the aggregation functions simultaneously using the method sum from the JavaScript Array object and the max/min functions of the JavaScript Math object. The reduce function will look similar to the following code:

function(key, values) {
  var explain = {total:Array.sum(values),
    max:Math.max.apply(Math, values),
    min:Math.min.apply(Math, values),
    avg:Array.sum(values)/values.length}
  return explain
}

For this example we will create synthetic data, randomly mixing the name of the 10 players and we will assign a random score between 0 and 100. Then, we will insert...