(PECL mongo >=0.9.2)
MongoCollection::group — Performs an operation similar to SQL's GROUP BY command
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).
Initial value of the aggregation counter object.
A function that aggregates (reduces) the objects iterated.
An condition that must be true for a row to be considered.
Returns an array containing the result.
Example #1 MongoCollection::group() example
<?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
$condition = array("a" => array( '$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 #2 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 MongoCollection::group() 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++; }'));
?>