old_aggregation.js

// Override group because map/reduce style is deprecated
DBCollection.prototype.agg_group = function( name, group_field, operation, op_value, filter ) {
    var ops = [];
    var group_op = { $group: { _id: '$' + group_field } };

    if (filter !== undefined) {
        ops.push({ '$match': filter });
    }

    group_op['$group'][name] = { };
    group_op['$group'][name]['$' + operation] = op_value;
    ops.push(group_op);

    return this.aggregate(ops);
};

// Function that groups and counts by group after applying filter
DBCollection.prototype.gcount = function( group_field, filter ) {
    return this.agg_group('count', group_field, 'sum', 1, filter);
};

// Function that groups and sums sum_field after applying filter
DBCollection.prototype.gsum = function( group_field, sum_field, filter ) {
    return this.agg_group('sum', group_field, 'sum', '$' + sum_field, filter);
};

// Function that groups and averages avg_feld after applying filter
DBCollection.prototype.gavg = function( group_field, avg_field, filter ) {
    return this.agg_group('avg', group_field, 'avg', '$' + avg_field, filter);
};