Converting keys of an array/object-tree to lowercase - php

Question

I am currently optimizing a PHP application and found one function being called around 10-20k times, so I'd thought I'd start optimization there:
function keysToLower($obj)
{
if(!is_object($obj) && !is_array($obj)) return $obj;
foreach($obj as $key=>$element)
{
$element=keysToLower($element);
if(is_object($obj))
{
$obj->{strtolower($key)}=$element;
if(!ctype_lower($key)) unset($obj->{$key});
}
else if(is_array($obj) && ctype_upper($key))
{
$obj[strtolower($key)]=$element;
unset($obj[$key]);
}
}
return $obj;
}
Most of the time is spent in recursive calls (which are quite slow in PHP), but I don't see any way to convert it to a loop.
What would you do?
This version doesn't account for associative arrays since my data doesn't have any, but is nearly 10 times faster than the original version. Most of the work was done by Gumbo, the major speedup comes from using references and creating a new object instead of unsetting the old keys.
function &keysToLower(&$obj)
{
if(is_object($obj))
{
$newobj = (object) array();
foreach ($obj as $key => &$val)
$newobj->{strtolower($key)} = keysToLower($val);
$obj=$newobj;
}
else if(is_array($obj))
foreach($obj as &$value)
keysToLower($value);
return $obj;
}

Answer 1

Foreach is using an internal copy that is then traversed. Try it without:
function keysToLower($obj)
{
$type = (int) is_object($obj) - (int) is_array($obj);
if ($type === 0) return $obj;
reset($obj);
while (($key = key($obj)) !== null)
{
$element = keysToLower(current($obj));
switch ($type)
{
case 1:
if (!is_int($key) && $key !== ($keyLowercase = strtolower($key)))
{
unset($obj->{$key});
$key = $keyLowercase;
}
$obj->{$key} = $element;
break;
case -1:
if (!is_int($key) && $key !== ($keyLowercase = strtolower($key)))
{
unset($obj[$key]);
$key = $keyLowercase;
}
$obj[$key] = $element;
break;
}
next($obj);
}
return $obj;
}
Or use references to avoid that a copy is used:
function &keysToLower(&$obj)
{
$type = (int) is_object($obj) - (int) is_array($obj);
if ($type === 0) return $obj;
foreach ($obj as $key => &$val)
{
$element = keysToLower($val);
switch ($type)
{
case 1:
if (!is_int($key) && $key !== ($keyLowercase = strtolower($key)))
{
unset($obj->{$key});
$key = $keyLowercase;
}
$obj->{$key} = $element;
break;
case -1:
if (!is_int($key) && $key !== ($keyLowercase = strtolower($key)))
{
unset($obj[$key]);
$key = $keyLowercase;
}
$obj[$key] = $element;
break;
}
}
return $obj;
}

Answer 2

You might also want to lookup array_change_key_case()

Answer 3

I assume you don't care about casting to array...
function keys_to_lower($o) {
if (is_object($o)) {
$o = (array)$o;
}
if (is_array($o)) {
return array_map('keys_to_lower', array_change_key_case($o));
}
else {
return $o;
}
}

Answer 4

here a example using lambda:
$multiArrayChangeKeyCase = function (&$array) use (&$multiArrayChangeKeyCase) {
$array = array_change_key_case($array);
foreach ($array as $key => $row)
if (is_array($row))
$multiArrayChangeKeyCase($array[$key]);
};

Answer 5

array_combine(array_map("strtolower", array_keys($a)), array_values($a))

Answer 6

A some what late response to a old thread but, there's a native function that does this, you could wrap it up something along these lines.
function setKeyCasing($thing, $case = CASE_LOWER) {
return array_change_key_case((array) $thing, $case);
}