MONGOCOLLECTION.GROUP(3)						 1						  MONGOCOLLECTION.GROUP(3)

MongoCollection::group - Performs an operation similar to SQL's GROUP BY command

SYNOPSIS

       public array MongoCollection::group (mixed  $keys, array  $initial, MongoCode  $reduce, [array  $options = array()])

DESCRIPTION

PARAMETERS

	      o $keys
		-  Fields  to group by. If an array or non-code object is passed, it will be the key used to group results. 1.0.4+: If $keys is an
		instance of MongoCode, $keys will be treated as a function that returns the key to group by (see the "Passing  a  $keys  function"
		example below).

	      o $initial
		- Initial value of the aggregation counter object.

	      o $reduce
		- A function that takes two arguments (the current document and the aggregation to this point) and does the aggregation.

	      o $options
		- Optional parameters to the group command. Valid options include:

		     o "condition" Criteria for including a document in the aggregation.

		     o "finalize" Function called once per unique key that takes the final output of the reduce function.

		     o "maxTimeMS"Specifies  a cumulative time limit in milliseconds for processing the operation (does not include idle time). If
		       the operation is not completed within the timeout period, a MongoExecutionTimeoutException will be thrown.

RETURN VALUES

	Returns an array containing the result.

CHANGELOG

       +--------+----------------------------------------------+
       |Version |					       |
       |	|					       |
       |	|		  Description		       |
       |	|					       |
       +--------+----------------------------------------------+
       | 1.5.0	|					       |
       |	|					       |
       |	|	   Added "maxTimeMS" option.	       |
       |	|					       |
       |1.2.11	|					       |
       |	|					       |
       |	|  Emits E_DEPRECATED when $options is scalar. |
       |	|					       |
       +--------+----------------------------------------------+
EXAMPLES

       Example #1

	      MongoCollection.group(3) example

	       This groups documents by category and creates a list of names within that category.

	      <?php

	      $collection->insert(array("category" => "fruit", "name" => "apple"));
	      $collection->insert(array("category" => "fruit", "name" => "peach"));
	      $collection->insert(array("category" => "fruit", "name" => "banana"));
	      $collection->insert(array("category" => "veggie", "name" => "corn"));
	      $collection->insert(array("category" => "veggie", "name" => "broccoli"));

	      $keys = array("category" => 1);

	      $initial = array("items" => array());

	      $reduce = "function (obj, prev) { prev.items.push(obj.name); }";

	      $g = $collection->group($keys, $initial, $reduce);

	      echo json_encode($g['retval']);

	      ?>

	      The above example will output something similar to:

	      [{"category":"fruit","items":["apple","peach","banana"]},{"category":"veggie","items":["corn","broccoli"]}]

       Example #2

	      MongoCollection.group(3) example

	       This example doesn't use any key, so every document will be its own group. It also uses a condition: only documents that match this
	      condition will be processed by the grouping function.

	      <?php

	      $collection->save(array("a" => 2));
	      $collection->save(array("b" => 5));
	      $collection->save(array("a" => 1));

	      // use all fields
	      $keys = array();

	      // set intial values
	      $initial = array("count" => 0);

	      // JavaScript function to perform
	      $reduce = "function (obj, prev) { prev.count++; }";

	      // only use documents where the "a" field is greater than 1
	      $condition = array('condition' => array("a" => array( '$gt' => 1)));

	      $g = $collection->group($keys, $initial, $reduce, $condition);

	      var_dump($g);

	      ?>

	      The above example will output something similar to:

	      array(4) {
		["retval"]=>
		array(1) {
		  [0]=>
		  array(1) {
		    ["count"]=>
		    float(1)
		  }
		}
		["count"]=>
		float(1)
		["keys"]=>
		int(1)
		["ok"]=>
		float(1)
	      }

       Example #3

	      Passing a $keys function

	       If  you	want  to  group  by  something	other  than  a	field name, you can pass a function as the first parameter of MongoCollec-
	      tion.group(3) and it will be run against each document. The return value of the function will be used as its grouping value.

	       This example demonstrates grouping by the num field modulo 4.

	      <?php

	      $c->group(new MongoCode('function(doc) { return {mod : doc.num % 4}; }'),
		   array("count" => 0),
		   new MongoCode('function(current, total) { total.count++; }'));

	      ?>

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