get random value from a PHP array, but make it unique

Question

I want to select a random value from a array, but keep it unique as long as possible.

For example if I'm selecting a value 4 times from a array of 4 elements, the selected value should be random, but different every time.

If I'm selecting it 10 times from the same array of 4 elements, then obviously some values will be duplicated.

I have this right now, but I still get duplicate values, even if the loop is running 4 times:

$arr = $arr_history = ('abc', 'def', 'xyz', 'qqq');

for($i = 1; $i < 5; $i++){
  if(empty($arr_history)) $arr_history = $arr; 
  $selected = $arr_history[array_rand($arr_history, 1)];  
  unset($arr_history[$selected]); 
  // do something with $selected here...
}

Answer 1

You almost have it right. The problem was the unset($arr_history[$selected]); line. The value of $selected isn't a key but in fact a value so the unset wouldn't work.

To keep it the same as what you have up there:

<?php

$arr = $arr_history = array('abc', 'def', 'xyz', 'qqq');

for ( $i = 1; $i < 10; $i++ )
{
  // If the history array is empty, re-populate it.
  if ( empty($arr_history) )
    $arr_history = $arr;

  // Select a random key.
  $key = array_rand($arr_history, 1);

  // Save the record in $selected.
  $selected = $arr_history[$key];

  // Remove the key/pair from the array.
  unset($arr_history[$key]);

  // Echo the selected value.
  echo $selected . PHP_EOL;
}

Or an example with a few less lines:

<?php

$arr = $arr_history = array('abc', 'def', 'xyz', 'qqq');

for ( $i = 1; $i < 10; $i++ )
{
  // If the history array is empty, re-populate it.
  if ( empty($arr_history) )
    $arr_history = $arr;

  // Randomize the array.
  array_rand($arr_history);

  // Select the last value from the array.
  $selected = array_pop($arr_history);

  // Echo the selected value.
  echo $selected . PHP_EOL;
}