Taking sum of “column” in MongoDB

Question

In MySQL, I would simply go \"SELECT sum(pts) FROM table\" to get the sum of the pts column on the table. However, I am converting this application to MongoDB and cannot fin

Answer 1

$mongo = new Mongo();

$map = new MongoCode("function() { emit('total', this.type); }");
$reduce = new MongoCode("function(k, vals) {
    var sum = 0;
    for(i in vals) {
        sum += vals[i];
    }

    return sum;
}");

$sumtotal = $mongo->db->command(array(
    'mapreduce' => 'tableName',
    'map' => $map,
    'reduce' => $reduce,
    // 'query' => array('col' => 'value'),
    'out' => array('merge' => 'tableName_sum')
));

$result = $mongo->db->selectCollection($sumtotal['result'])->findOne();
$sum = $result['value'];