PHP: Check for duplicate values in a multidimensional array

Question

I have this issue with multidimensional arrays.

Given the following multidimensional array:

Array(
[0] => Array("a", "b", "c")
[1] => Array("x", "y", "z")
[2] => Array("a", "b", "c")
[3] => Array("a", "b", "c")
[4] => Array("a", "x", "z")
)

I want to check its values and find duplicates (i.e. keys 0, 2 and 3) leaving just one key - value pair deleting the others, resulting in somthing like this:

Array(
    [0] => Array("a", "b", "c")
    [1] => Array("x", "y", "z")
    [2] => Array("a", "x", "z")
    )

How can I do that??

Try http://php.net/manual/en/function.array-unique.php it should help you. — enam
– enam, Commented Feb 9, 2011 at 18:38

score 17 · Accepted Answer · 2014-03-11 11:24:19Z

17

This will remove duplicate items from your array using array_unique():

$new_arr = array_unique($arr, SORT_REGULAR);

edited Mar 11, 2014 at 11:24

answered Feb 9, 2011 at 18:39

user142162

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8 Comments

Artefacto Over a year ago

-1 Look at the docs. This will convert the values of the array to strings before comparing.

user142162 Over a year ago

@Artefacto: Look at the docs. I'm using the SORT_REGULAR flag which does NOT use string comparison.

enam Over a year ago

as per php document "Note that array_unique() is not intended to work on multi dimensional arrays.". It can be seen from the given link.

Artefacto Over a year ago

@enam I think it just means that array_unique doesn't flatten the array to find the uniques. (btw, +1)

Maldoror Over a year ago

Thought array_unique doesn't work with multidimensional arrays.

|

JF Dion · Accepted Answer · 2011-02-09 18:38:23Z

8

You can simply do it using in_array()

$data = Array(
    0 => Array("a", "b", "c"),
    1 => Array("x", "y", "z"),
    2 => Array("a", "b", "c"),
    3 => Array("a", "b", "c"),
    4 => Array("a", "x", "z"),
);

$final = array();
foreach ($data as $array) {
    if(!in_array($array, $final)){
        $final[] = $array;
    }
}

which will get you something like

array(3) {
  [0] => array(3) {
    [0] => string(1) "a"
    [1] => string(1) "b"
    [2] => string(1) "c"
  }
  [1] => array(3) {
    [0] => string(1) "x"
    [1] => string(1) "y"
    [2] => string(1) "z"
  }
  [2] => array(3) {
    [0] => string(1) "a"
    [1] => string(1) "x"
    [2] => string(1) "z"
  }
}

answered Feb 9, 2011 at 18:38

JF Dion

4,0542 gold badges26 silver badges35 bronze badges

Comments

Gediminas · Accepted Answer · 2011-02-09 19:13:51Z

1

You can go smart with serialization for comparison of arrays.

var_dump(makeUnique($data));

function makeUnique(array $data)
{
    $serialized = array_map(create_function('$a', 'return serialize($a);'), $data);
    $unique = array_unique($serialized);
    return array_intersect_key($unique, $data);
}

Have fun

answered Feb 9, 2011 at 19:13

Gediminas

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Comments

Artefacto · Accepted Answer · 2011-02-09 19:07:06Z

0

$arr = ...;
$final = array();
sort($arr);
foreach ($arr as $el) {
   if (!isset($prev) || $el !== $prev)
       $final[] = $el
    $prev = $el;
}

This is a more efficient¹ solution (log n + n instead of quadratic) but it relies on a total order between all the elements of the array, which you may not have (e.g. if the inner arrays have objects).

¹ More efficient than using in_array. Turns out array_unique actually uses this algorithm, so it has the same shortcomings.

edited Feb 9, 2011 at 19:07

answered Feb 9, 2011 at 18:54

Artefacto

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Comments

Bob Jansen · Accepted Answer · 2013-11-16 14:44:53Z

0

To check using array_unique on multidimensional arrays, you need to flatten it out like so, using implode.

    $c=count($array)
    for($i=0;$i<$c;$i++)
    {
    $flattened=implode("~",$array[$i]);
    $newarray[$i]=$flattened;
     }
    if(count(array_unique($newarray)
    <count($newarray))
    {
    //returns true if $array contains duplicates
    //can also use array_unique on $newarray 
    //to remove   duplicates, then explode, 
    //to return to default state
    }

Hope this is helpful, took sometime to get it.

edited Nov 16, 2013 at 14:44

Bob Jansen

8911 bronze badges

answered Jan 29, 2013 at 14:10

Mrdexed

1

1 Comment

j0k Over a year ago

Could you fix encoding mistake 〓 ?

Isuru U Liyana Arachchi · Accepted Answer · 2021-11-15 13:56:39Z

**This is example array**
$multi_com=[
    [
        {
            "combination_id": "19"
        },
        {
            "combination_id": "20"
        },
        {
            "combination_id": "21"
        }
    ],
    [
        {
            "combination_id": "18"
        },
        {
            "combination_id": "20"
        },
        {
            "combination_id": "22"
        }
    ],
    [
        {
            "combination_id": "20"
        },
        {
            "combination_id": "21"
        }
    ]
]

**This is sample code**
        $array1 = [];
        $array2 = [];
        $status = false;
        foreach ($multi_com as $key => $val) {
            foreach ($val as $key2 => $val2) {
                if (count($array1) !== 0) {
                    $array_res = in_array($val2->combination_id, $array1);
                    if ($array_res) {
                        $array2[] = $val2->combination_id;
                    }
                }
            }

            if (!$status) {
                for ($x = 0; $x < count($val); $x++) {
                    $array1[] = $val[$x]->combination_id;
                }
            } else {
                $array1 = [];
                $array1 = $array2;
                $array2 = [];
            }
            $status = true;
        }

        return $array1;

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