(PECL mongo >=0.9.0)
MongoCollection::deleteIndex — Deletes an index from this collection
$keys
   ) : arrayThis method is identical to:
<?php
public function deleteIndexes($keys) {
  $indexName = $this->toIndexString($keys);
  return $this->db->command(array(
    "deleteIndexes" => $this->getName(),
    "index" => $indexName,
  ));
}
?>
   Each index is given a unique name when it is created. This is often generated
   by the driver based on the index key(s) and order/type, but custom names may
   also be specified with MongoCollection::createIndex()'s
   "name" option).
  
   Unfortunately, MongoCollection::deleteIndex() cannot
   delete custom-named indexes due to a backwards compatibility issue. When a
   string argument is provided, it is assumed to be the single field name in an
   ascending index (e.g. the name "x_1" would be used for the
   argument "x"). If an array or object is provided, an index
   name is generated just as if that argument was passed to
   MongoCollection::createIndex().
  
   In order to delete a custom-named index with the PHP driver, the
   deleteIndexes database command must be used. For instance,
   an index named "myIndex" could be deleted with the PHP driver by running:
  
<?php
$db->command(array(
  "deleteIndexes" => $collection->getName(),
  "index" => "myIndex",
));
?>
   To determine the name of an index with the PHP driver, you can query the
   system.indexes collection of a database and look for the
   "name" field of each result. The "ns"
   field will indicate the collection to which each index belongs.
  
keys
     
       An array specifying the index's fields as its keys. For each field, the
       value is either the index direction or
       » index type.
       If specifying direction, specify 1 for ascending or
       -1 for descending.
      
If a string is provided, it is assumed to be the single field name in an ascending index.
Returns the database response.
Example #1 MongoCollection::deleteIndex() example
This example passes the function string and array parameters.
<?php
$m = new MongoClient();
$c = $m->example->indices;
// create and remove a simple index
$c->createIndex(array("i"=>1));
$c->deleteIndex("i");
// create and remove a multi-key index
$c->ensureIndex(array("j" => 1, "k" => 1));
$c->deleteIndex(array("j" => 1, "k" => 1));
?>