注意：未定义偏移量：＃从数组中检索和删除值时

Question

I sometimes (not all the time) get this Notice: Undefined offset: # error

I have an array of words. I am randomly selecting a word from this array and then deleting it. The word that I retrieve from the word array is then placed into another array.

$numberOfWords = $_POST['number_of_words'];
$words = array('an', 'array', 'of', 'words', 'to', 'select', 'from');
$selectedWords = array();

for($i = 0; $i < $numberOfWords; $i++) {
  $wordAt = rand(0, count($words) - 1);
  $word = $words[$wordAt];
  array_push($selectedWords, $word);
  unset($words[$wordAt]);
}

Any ideas?

Thanks!

Answer 1

The issue is that unsetting an array element does not magically renumber the array keys. You wind up with a hole in the array. Your random number generator doesn't take this into account, and you will wind up selecting the same index multiple times causing your undefined index notice. You can easily pick out a random array element using array_rand :

for($i = 0; $i < $numberOfWords; $i++) {
  $word = array_rand($words);
  array_push($selectedWords, $words[$word]);
  unset($words[$word]);
}

Answer 2

After unset an array element, we need to rebuild the array index using array_values :

$numberOfWords = $_POST['number_of_words'];
$words = array('an', 'array', 'of', 'words', 'to', 'select', 'from');
$selectedWords = array();

for($i = 0; $i < $numberOfWords; $i++) {
  $wordAt = rand(0, count($words) - 1);
  $word = $words[$wordAt];
  array_push($selectedWords, $word);
  unset($words[$wordAt]);
  $words = array_values($words);
}