Demo für http://www.phpgangsta.de/kleine-aufgabe-ein-array-umbauen

ArrayDemo.php

function mergeNumbers($numbers) {
    $newNumbers = array();

    reset($numbers);

    while(($currentNumber = current($numbers)) !== false) {
      $tmpCurrent = $currentNumber;
      while (($nextNumber = next($numbers)) !== false && abs($nextNumber-$tmpCurrent)==1) {
          $tmpCurrent = $nextNumber;
      }

      if ($tmpCurrent == $currentNumber) {
          $newNumbers[] = $currentNumber;
      }
      else {
          $newNumbers[] = $currentNumber . '-' . $tmpCurrent;
      }
    }

    return $newNumbers;
}

function splitNumbers($numbers) {
    $newNumbers = array();

    foreach($numbers as $number) {
        if (strpos($number, '-')) {
            $range = explode('-', $number, 2);
            array_splice($newNumbers, count($newNumbers), 0, range($range[0], $range[1]));
        }
        else {
            $newNumbers[] = $number;
        }
    }

    return $newNumbers;
}

$numbers = array(13,81,80,79,78,77,76,19,40,41,42,43,44,45,48);

$numbers = mergeNumbers($numbers);
var_dump($numbers);

$numbers = splitNumbers($numbers);
var_dump($numbers);