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php – case-insensitive array_unique

Posted by: admin April 23, 2020 Leave a comment


I’m trying to write a few lines of code to make a case insensitive array unique type function. Here’s what I have so far:

foreach ($topics as $value) {
    $lvalue = strtolower($value);
    $uvalue = strtolower($value);

    if (in_array($value, $topics) == FALSE || in_array($lvalue, $topics) == FALSE || in_array($uvalue, $topics) == FALSE) {
        array_push($utopics, $value);

The trouble is the if statement. I think there’s something wrong with my syntax, but I’m relatively new to PHP and I’m not sure what it is. Any help?

How to&Answers:
function array_iunique( $array ) {
    return array_intersect_key(
        array_unique( array_map( "strtolower", $array ) )


You’re setting both lvalue and uvalue to the lower case version.

 $uvalue = strtolower($value);

should be

 $uvalue = strtoupper($value);

That said, this might be a little faster. The performance of your function will degrade exponentially, while this will be more or less linear (at a guess, not a comp-sci major…)


function array_iunique($ar) {
  $uniq = array();
  foreach ($ar as $value)
    $uniq[strtolower($value)] = $value;
  return array_values($uniq);


Should $uvalue not be uppercase?

$uvalue = strtoupper($value):


and another alternative…

function array_iunique($topics) {

    $ltopics = array_map('strtolower', $topics);
    $cleanedTopics = array_unique($ltopics);

    foreach($topics as $key => $value) {
        if(!isset($cleanedTopics[$key])) {

    return $topics;


Pentium10’s is better though.