Identify most common extension in an Array - php

Question

Take the following code into consideration:
$files = array('1.js', '1.css', '2.js', '2.css', '3.js', '3.png');
$extensions = array();
foreach ($files as $file)
{
$extension = strtolower(pathinfo($file, PATHINFO_EXTENSION));
if (empty($extensions[$extension]) === true)
{
$extensions[$extension] = 0;
}
++$extensions[$extension];
}
arsort($extensions); // array('js' => 3, 'css' => 2, 'png' => 1)
$common_extension = key($extensions); // js
The code seems to work as I want it to (I still need to check what happens in case there is a draw, but that's irrelevant for this question). I'm looking for a more efficient (and compact way) of rewriting the above snippet, the closest I've got so far is:
$files = array('1.js', '1.css', '2.js', '2.css', '3.js', '3.png');
$extensions = array_count_values(array_map('strtolower', preg_replace('~^.*[.](.*)$~', '$1', $files)));
arsort($extensions, SORT_NUMERIC);
$common_extension = key($extensions);
But this loops through the array 3 times and that preg_replace() is not bulletproof... Any ideas?

Answer 1

I would do something like this:
<?php
function getCommon($array, $result = array()) {
foreach ($array as $k => $v) { $array[$k] = strtolower(pathinfo($v, PATHINFO_EXTENSION)); }
$ext = array_count_values($array); arsort($ext,SORT_NUMERIC);
$k = array_keys($ext); $k0 = $k[0];
if ($ext[$k0] > $ext[$k[1]]) { $result[] = $k0; }
else { foreach ($ext as $k => $v) { if ($v == $ext[$k0]) { $result[] = $k; } } }
return $result;
}
$files = array('1.js', '2.js', '3.png', '4.css');
print_R($files);
print_R(getCommon($files));
$files2 = array('1.js', '2.js', '3.png', '4.png', '5.css');
print_R($files2);
print_R(getCommon($files2));
?>
This will return an array, where values will be common extensions, even if they are many.
Note: Don't use regex when your job basic PHP functions can do - regex is too resource-consuming compared to php built-in functions.

Answer 2

I have thought about this question for quite some time now and I think your first snippet is pretty much the answer to it. It is not like shorter code is faster code. That code is pretty fast and scaling linearly to greater arrays. It is pretty much a complexity of O(n) plus the sorting algorithm arsort (i have no clue what method it is using, but i expect it to be faster than a self written one). The only thing I can offer is this little function containing your snippets and a little tweak in the case the extension is not in the array.
function count_ext($array){
$ret = array();
foreach($array as $ext){
$ext = strtolower(pathinfo($ext, PATHINFO_EXTENSION));
if( !isset($ret[$ext]) ) $ret[$ext] = 0;
$ret[$ext]++;
}
arsort($ret);
return $ret;
}
I don't know how many elements your arrays have and how time-critical your use case is, but this method will do well.