GROUP BY in MongoDB

mongodb-aggregation.php

<?php

$mongo = new Mongo('mongodb://localhost', array('persist' => true));
$collection = $mongo->selectDB('test')->selectCollection('group');
$collection->drop();

foreach (range(1,1000) as $i){
  $name = ($i % 3 === 0) ? 'Fred' : 'Bob';
  $collection->insert(array('id' => $i, 'name' => $name));
}

$collection->ensureIndex(array('name' => true));

// http://www.php.net/manual/en/mongocollection.group.php
$cursor = $collection->group(
  array('name' => true), // fields to group by
  array('count' => 0), // initial value of the aggregation counter object. 
  new MongoCode('function(doc, prev) { prev.count += 1 }'), // a function that takes two arguments (the current document and the aggregation to this point) and does the aggregation
  array('id' => array('$gt' => 200)) // condition for including a document in the aggregation
  );
  
print 'Total: ' . $cursor['count'] . "\n";
foreach ($cursor['retval'] as $item)
  print "\t" . $item['name'] . ': ' . $item['count'] . "\n";

This example is very helpfull. Thanks!