PHP array unique by column

Question

How to filter an array to give unique elements according to one or more columns. Example:

array(
    array('name'=>'toto', 'type'=>'1', 'type2'=> '2')
    array('name'=>'tata', 'type'=>'1', 'type2'=> '3')
    array('name'=>'titi', 'type'=>'1', 'type2'=> '2')
    array('name'=>'tutu', 'type'=>'2', 'type2'=> '4')
    array('name'=>'tete', 'type'=>'3', 'type2'=> '2')
)

If we choose type and type2 as the unique column. The result of the algorithm should gives

array(
    array('name'=>'toto', 'type'=>'1', 'type2'=> '2')
    array('name'=>'tata', 'type'=>'1', 'type2'=> '3')
    array('name'=>'tutu', 'type'=>'2', 'type2'=> '4')
    array('name'=>'tete', 'type'=>'3', 'type2'=> '2')
)

I can think of an algorithm by hashing the type concatenate with type2, store in a table and using isset to find the existence. But I'm not sure that's the best algorithm.

How does your algorithm decide which of titi or toto to discard? — Kevin Brydon
– Kevin Brydon, Commented May 7, 2013 at 12:46
You need to get unique values according to 'type2'?How to decide titi or toto is needed? — Shijin TR
– Shijin TR, Commented May 7, 2013 at 12:47
why not just do this in a database with unique column constraints? — Jakub
– Jakub, Commented May 7, 2013 at 12:50
@KevinBrydon Let's just say by default we take the first found array. In this case is toto array. Or if possible I want also a version that take the last found array. @Jakub: in my case, the data doesn't necessary come from a dump of SQL — Thanh Trung
– Thanh Trung, Commented May 7, 2013 at 13:04
Can anyone provide an answer here that does not use foreach and assignment, but is instead based on a map/filter/reduce implementation using PHP's array functions? — Nicholas Shanks
– Nicholas Shanks, Commented Mar 8, 2017 at 17:15

Baba · Accepted Answer · 2013-05-07 14:39:33Z

2

All you need is

$data = array(
    array('name'=>'toto', 'type'=>'1', 'type2'=> '2'),
    array('name'=>'tata', 'type'=>'1', 'type2'=> '3'),
    array('name'=>'titi', 'type'=>'1', 'type2'=> '2'),
    array('name'=>'tutu', 'type'=>'2', 'type2'=> '4'),
    array('name'=>'tete', 'type'=>'3', 'type2'=> '2')
);


$tmp = array();
foreach($data as $v) {
    $id = $v['type'] . "|" . $v['type2'];
    isset($tmp[$id]) or $tmp[$id] = $v;
}
print_r(array_values($tmp));

edited May 7, 2013 at 14:39

answered May 7, 2013 at 12:50

Baba

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8 Comments

Thanh Trung Over a year ago

Same as above, this only check for uniqueness of type2, I also want a comparison with type too

Thanh Trung Over a year ago

Your version only works in this special case... If I add array('name'=>'tete', 'type'=>'3', 'type2'=> '2') it's not gonna work...

Thanh Trung Over a year ago

Your solution is what I said in my post :

I can think of an algorithm by hashing the type concatenate with type2, store in a table and using isset to find the existence. But I'm not sure that's the best algorithm.

Actually, it would better if you hash your $id with md5()

Baba Over a year ago

Keep it simple .... alternatives would be to use array_reduce might not be as readable or faster ....

Tasso Evangelista Over a year ago

'type'=>'11', 'type2'=> '3' can't be equivalent to 'type'=>'1', 'type2'=> '13'?

|

Tasso Evangelista · Accepted Answer · 2013-05-07 12:59:55Z

2

$arr = array(
    array('name'=>'toto', 'type'=>'1', 'type2'=> '2'),
    array('name'=>'tata', 'type'=>'1', 'type2'=> '3'),
    array('name'=>'titi', 'type'=>'1', 'type2'=> '2'),
    array('name'=>'tutu', 'type'=>'2', 'type2'=> '4')
);

$filtered = array(); // resulting array
$combinations = array(); // combinations of 'type' and 'type2' values

foreach ( $arr as $elem ) {

    $comb = array($elem['type'], $elem['type2']);

    if ( !in_array($comb, $combinations) ) { // new combination
        $combinations[] = $comb;
        $filtered[] = $elem;
    }
}

answered May 7, 2013 at 12:59

Tasso Evangelista

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1 Comment

Thanh Trung Over a year ago

This one works too. But same as above, in_array is overkill

deceze · Accepted Answer · 2013-05-07 13:16:52Z

2

$keys = array('type', 'type2');
$filtered = array();

foreach ($array as $elem) {
    $compKey = join('|', array_intersect_key($elem, array_flip($keys)));
    $filtered[$compKey] = $elem;
}

// optionally: $filtered = array_values($filtered);

edited May 7, 2013 at 13:16

answered May 7, 2013 at 12:47

deceze♦

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5 Comments

Tasso Evangelista Over a year ago

Although generates the example result array, it only uses 'type2' as criteria, and OP required uniqueness based in 'type' column too.

deceze Over a year ago

Maybe true. The question is a bit too vague how exactly the algorithm should behave. I just read it as "choose one or the other".

Thanh Trung Over a year ago

Both type and type2 are required, sorry. Unique column is easy, I wouldn't ask...

deceze Over a year ago

@Thanh Then joining all values of all keys by some separator and use it as composite key should do the trick. Updated answer.

Thanh Trung Over a year ago

@deceze Result found will be : titi, tata, tutu, tete. Which is good enough for me. One small problem is that titi position is changed. Having titi after tata is perfect because we keep the order. Or is possible to replace titi with toto ?

Atle · Accepted Answer · 2013-05-07 13:32:38Z

1

Updated to support key combinations

<?php

$array=array(
    array('name'=>'toto', 'type'=>'1', 'type2'=> '2'),
    array('name'=>'tata', 'type'=>'1', 'type2'=> '3'),
    array('name'=>'titi', 'type'=>'1', 'type2'=> '2'),
    array('name'=>'tutu', 'type'=>'2', 'type2'=> '4'),
);

function filter($key,$array){
    $filtered=array();
    $used=array();
    foreach ($array as $e){
        $v=array();
        foreach ($key as $k) $v[]=$e[$k];
        if (!in_array($v,$used)){
            $used[]=$v;
            $filtered[]=$e;
        }
    }
    return $filtered;
}

$filtered=filter(array('type2','type'),$array);

edited May 7, 2013 at 13:32

answered May 7, 2013 at 12:53

Atle

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4 Comments

Atle Over a year ago

Which it is supposed to do when filtering on 'type'. Filtering on 'type2' will remove 'titi'. Second run, filtering on 'type' will remove tata.

Thanh Trung Over a year ago

Yes, but it doesn't give the same result I want. The unique constraint is a couple (type, type2) not just one or another

Thanh Trung Over a year ago

Thanks, it worked. One problem is performance. Using in_array is overkill when you have 10k line of record for example. Try to use less function call as possible. The number of loop is nb_field_unique * array_size²

Atle Over a year ago

Now you want optimized as well? :-) The solutions using keys will be faster then, since the keys are hashtables and thus O(1).

lov3catch · Accepted Answer · 2022-11-07 13:01:17Z

What about this way?

Result array is not the same as that of the author. But still valid for the condition:

...filter an array to give unique elements according to one or more columns.

<?php

declare(strict_types=1);

$input = [
    ['name' => 'toto', 'type' => '1', 'type2' => '2'],
    ['name' => 'tata', 'type' => '1', 'type2' => '3'],
    ['name' => 'titi', 'type' => '1', 'type2' => '2'],
    ['name' => 'tutu', 'type' => '2', 'type2' => '4'],
    ['name' => 'tete', 'type' => '3', 'type2' => '2'],
];

$keys = array_map(
    static fn(string $key, string $value) => "$key:$value",
    array_column($input, 'type'), array_column($input, 'type2'));

$result = array_values(array_combine($keys, array_values($input)));

$expect = [
    ['name' => 'titi', 'type' => '1', 'type2' => '2'],
    ['name' => 'tata', 'type' => '1', 'type2' => '3'],
    ['name' => 'tutu', 'type' => '2', 'type2' => '4'],
    ['name' => 'tete', 'type' => '3', 'type2' => '2'],
];

assert($result === $expect); // true

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