How to Use Array_Unique on an Array of Arrays

How do I use array_unique on an array of arrays?

It's because array_unique compares items using a string comparison. From the docs:

Note: Two elements are considered
equal if and only if (string) $elem1
=== (string) $elem2. In words: when the string representation is the same.
The first element will be used.

The string representation of an array is simply the word Array, no matter what its contents are.

You can do what you want to do by using the following:

$arr = array(
    array('user_id' => 33, 'frame_id' => 3),
    array('user_id' => 33, 'frame_id' => 3),
    array('user_id' => 33, 'frame_id' => 8)
);

$arr = array_intersect_key($arr, array_unique(array_map('serialize', $arr)));

//result:
array
  0 => 
    array
      'user_id' => int 33
      'user' => int 3
  2 => 
    array
      'user_id' => int 33
      'user' => int 8

Here's how it works:

Each array item is serialized. This
will be unique based on the array's
contents.
The results of this are run through array_unique,
so only arrays with unique
signatures are left.
array_intersect_key will take
the keys of the unique items from
the map/unique function (since the source array's keys are preserved) and pull
them out of your original source
array.

array_unique for arrays inside array

You should modify your call for array_unique to have it include the SORT_REGULAR flag.

$arr2 = array_unique($arr, SORT_REGULAR);

How to remove duplicate values from a multi-dimensional array in PHP

Here is another way. No intermediate variables are saved.

We used this to de-duplicate results from a variety of overlapping queries.

$input = array_map("unserialize", array_unique(array_map("serialize", $input)));

How can you get unique values from multiple arrays using array_unique?

The answer to the first part of your question is NO.

The array_unique function definition in the PHP manual states that array_unique takes exactly two arguments, one array, and an optional integer that determines the sorting behavior of the function.

array array_unique ( array $array [, int $sort_flags = SORT_STRING ] )

Rather than take the manual's word for it, here are some test arrays.

$one_array      = ['thing', 'another_thing', 'same_thing', 'same_thing'];
$two_arrays     = ['A', 'B', 'C', 'thing', 'same_thing'];
$or_more_arrays = ['same_thing', 1, 2, 3];

A couple of test show that the function does work as advertised:

$try_it = array_unique($one_array);

returns ['thing', 'another_thing', 'same_thing'];

$try_it = array_unique($one_array, $two_arrays);

gives you a warning

Warning: array_unique() expects parameter 2 to be integer, array given

and returns null.

$try_it = array_unique($one_array, $two_arrays, $or_more_arrays);

also gives you a warning

Warning: array_unique() expects at most 2 parameters, 3 given

and returns null.

The answer to the second part of your question is YES.

To get unique values using array_unique, you do have to have one array of values. You can do this, as u_mulder commented, by using array_merge to combine the various input arrays into one before using array_unique.

$unique = array_unique(array_merge($one_array, $two_arrays, $or_more_arrays));

returns

['thing', 'another_thing', 'same_thing', 'A', 'B', 'C', 1, 2, 3];

If instead of several individual array variables, you have an array of arrays like this:

$multi_array_example = [
    [1, 2, 3],
    [2, 3, 4], 
    [3, 4, 5],
    [4, 5, 6]
];

Then you can unpack the outer array into array merge to flatten it before using array_unique.

$unique = array_unique(array_merge(...$multi_array_example));

Or in older PHP versions (<5.6) before argument unpacking, you can use array_reduce with array_merge.

$unique = array_unique(array_reduce($multi_array_example, 'array_merge', []));

returns [1, 2, 3, 4, 5, 6]

array unique for multi dimensional array in php

Why are you making it so hard,

 $in = array (
    1 => 
    array (
        'country' => 'US',
        'state' => 'Albama',
        'city' => 'Brest',
        'postcode' => '225001-225003',
        'shipping_info' => 'DeliveryAvailable',
        'is_zip_range' => 1,
        'zip_from' => 225001,
        'zip_to' => 225003
    ),
    2 => 
    array (
        'country' => 'BY',
        'state' => 'Brest',
        'city' => 'Brest',
        'postcode' => '225001-225003',
        'shipping_info' => 'DeliveryAvailable',
        'is_zip_range' => 1,
        'zip_from' => 225001,
        'zip_to' => 225003
    )
);

$out = [];
foreach($in as $i) if(!isset($out[$i['postcode']])) $out[$i['postcode']] = $i;

Sandbox

You can do the same thing with in_array, but the isset is faster.

In fact you dont even need to do the isset

foreach($in as $i) $out[$i['postcode']] = $i;

Array keys are always unique, but this will retain the last duplicate where as the previous code keeps the first one.

And if the keys bug you latter just do $out = array_values($out) to reset them.

array_unique for objects?

Well, array_unique() compares the string value of the elements:

Note: Two elements are considered equal if and only if (string) $elem1 === (string) $elem2 i.e. when the string representation is the same, the first element will be used.

So make sure to implement the __toString() method in your class and that it outputs the same value for equal roles, e.g.

class Role {
    private $name;

    //.....

    public function __toString() {
        return $this->name;
    }

}

This would consider two roles as equal if they have the same name.

array_unique inconsistent for simple arrays

array_unique([1,2,3,4,4]) returns:

array(4) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
  [3]=>
  int(4)
}

Note that the keys are sequential

While array_unique([1,2,3,3,4])) returns:

array(4) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
  [4]=>
  int(4)
}

Note the jump between the key 2 and the key 4.

Because of that - json_encode will omit the keys in the first array (and keep it as array object), while in the second array - the json_encode will look at your array as object and will keep the keys.

You can use array_values (to get the values and ignore the keys).

How to remove duplicate values from an array in PHP

Use array_unique().

Example:

$array = array(1, 2, 2, 3);
$array = array_unique($array); // Array is now (1, 2, 3)

PHP array_unique is converted to object

The function array_unique() filters out equal values so the reason why #3 of the index is missing is because its equal to #0.

You can re-index the array with array_values():

var_dump(array_values(array_unique($errors, SORT_REGULAR)));

JavaScript perceives PHP's associative array's as an object because it only understands numeric keyed arrays.

You should be using json to communicate between both languages:

echo json_encode($errors);

As this would cause in javascript the outer the value to be turned into an array and turn each item into an object.

var arr = JSON.parse(outputofjson_encode);

console.log(arr[0].id);