mb_count_chars.php

<?php

/**
 * mb_count_chars
 * @author @memory-agape
 * @param string $string The examined string
 * @param int $mode 
 * @return array|string 
 */
function mb_count_chars ($string, $mode = 0) {
    
    $result =  array_fill(0, 256, 0);
    
    for ($i = 0, $size = mb_strlen($string); $i < $size; $i++) {
        $char = mb_substr($string, $i, 1);
        if (strlen($char) > 1) {
            continue;
        }
        
        $code = ord($char);
        if ($code >= 0 && $code <= 255) {
            $result[$code]++;
        }
    }
    
    switch ($mode) {
        case 1: // same as 0 but only byte-values with a frequency greater than zero are listed.
            foreach ($result as $key => $value) {
                if ($value == 0) {
                    unset($result[$key]);
                }
            }
            break;
        case 2: // same as 0 but only byte-values with a frequency equal to zero are listed.
            foreach ($result as $key => $value) {
                if ($value > 0) {
                    unset($result[$key]);
                }
            }
            break;
        case 3: // a string containing all unique characters is returned.
            $buildString = '';
            foreach ($result as $key => $value) {
                if ($value > 0) {
                    $buildString .= chr($key);
                }
            }
            return $buildString;
        case 4: // a string containing all not used characters is returned.
            $buildString = '';
            foreach ($result as $key => $value) {
                if ($value == 0) {
                    $buildString .= chr($key);
                }
            }
            return $buildString;
    }
    
    // change key names...
    foreach ($result as $key => $value) {
        $result[chr($key)] = $value;
        unset($result[$key]);
    }
    
    return $result;
    
}

Hello

Nice function. FYI: I have created a library including mb_count_chars: https://github.com/MathiasReker/php-mbstring-extension