Removing duplicate entries from an array with PHP

Question

I have an array that looks like this when I use var_dump:

array(4) {
  [0]=> array(2) { 
    [0]=> string(1) "1"
    ["userID"]=> string(1) "1" 
  }
  [1]=> array(2) {
    [0]=> string(1) "2" 
    ["userID"]=> string(1) "2"
  }
  [2]=> array(2) { 
    [0]=> string(1) "1"
    ["userID"]=> string(1) "1"
  } 
  [3]=> array(2) {
    [0]=> string(1) "1"
    ["userID"]=> string(1) "1"
  }
}

That is 1,2,1,1

I tried using array_unique($arr) but on this particular array, instead of turning it into 1,2, it just turns the array into 1.

It should work, but I'm not sure why it doesn't.

What is the resultant array that you are looking for? "turning [the array] into 1,2" doesn't make much sense to me. — erisco
– erisco, Commented Mar 23, 2011 at 22:41

Damon · Accepted Answer · 2011-03-23 22:10:28Z

4

array_unique only removes elements that are equal by their string value. That is not the case for sub-arrays.

You will need to iterate over the array manually (after sorting with a user function) and unset the doubles. Not pretty, sorry.

answered Mar 23, 2011 at 22:10

Damon

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1 Comment

erisco Over a year ago

I don't think he needs to, but it is an option.

erisco · Accepted Answer · 2011-03-23 23:06:28Z

I am going to guess that all you care about is knowing which userIDs exist in the result set. Therefore, I will flatten the array first. After doing so, I can apply array_unique to obtain only the unique values. As others have stated, array_unique is not designed to work with multidimensional arrays.

$flattened = array_map(
  function($e) { return $e['userID']; },
  $array
);
$unique = array_unique($flattened);

If you like foreach loops, then it would look like this.

$flattened = array();
foreach ($array as $v) {
    $flattened[] = $v['userId'];
}
$unique = array_unique($flattened);

There is also an alternative to finding unique elements which offers a performance boost over array_unique -- O(n) time complexity versus O(nlogn). That is, array_unique($array) is equivalent to array_keys(array_flip($array)).

Arc · Accepted Answer · 2011-03-24 09:28:43Z

2

A kind of quick and dirty method might be to iterate over all elements, serialize the values and use these as keys in a new array that contains their values as well then use array_values() on that array like this:

<?php
function array_unique_recursive(array $a) {
    $result = array();
    foreach ($a as $item)
        $result[serialize($item)] = $item;
    return array_values($result);
}
?>

edited Mar 24, 2011 at 9:28

answered Mar 23, 2011 at 22:45

Arc

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Comments

Mahesh · Accepted Answer · 2011-03-24 16:36:07Z

0

<?php
$arr = array(
               array ( 0=>"1",
                        userID=>"1"),
                array ( 0=>"2",
                        userID=>"2"),
        array ( 0=>"1",
                        userID=>"1"),
        array ( 0=>"1",
                        userID=>"1"));

    $arr_unique=array_unique($arr);
    echo '<pre>';
    var_dump($arr_unique);
    echo '</pre>';
?>

edited Mar 24, 2011 at 16:36

Mahesh

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answered Mar 24, 2011 at 5:59

Revathi

1

Comments

Uzair Bin Nisar · Accepted Answer · 2012-12-20 07:41:18Z

0

Try using sort regular filter ... <?php $arr = array_unique($arr, SORT_REGULAR); ?>

answered Dec 20, 2012 at 7:41

Uzair Bin Nisar

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