Add duplicated values of a php array to another and keep the same keys

Question

I have a PHP Array, and I want to extract from it the duplicated values and keep the corresponding keys for each value, in a new Array.

This is my starting Array

Array
(
    [0] => ABC123-A
    [1] => BG231-B
    [2] => ABC123-A
    [3] => BG231-E
    [4] => BG231-F
    [5] => BG231-G
    [6] => BG231-H
    [7] => ABC123-A
    [8] => BG231-J
    [9] => BG231-K
    [10] => ABC123-A
)

And this is what I want to have:

Array
(
    [0] => ABC123-A
    [2] => ABC123-A
    [7] => ABC123-A
    [10] => ABC123-A
)

How can I do that ?

Thanks for help.

I have more than one duplicated value, I want to keep them (with the corresponding key), because I need these values... — Dali
– Dali, Commented May 3, 2012 at 13:36
This answer get's you all duplicated values - every duplicate value has it's own array and is keyed by the value. Each array contains the original keys. — hakre
– hakre, Commented May 3, 2012 at 13:40

hakre · Accepted Answer · 2012-05-04 00:10:33Z

1

Test this out:

$return = array_unique($array);
var_dump(
    array_diff($array, array_diff($return, array_diff_assoc($array, $return)))
);

edited May 4, 2012 at 0:10

hakre

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answered May 3, 2012 at 13:20

Makkesk8

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Comments

hakre · Accepted Answer · 2012-05-03 13:25:43Z

PHP has no function build in that does this, but you can combine array_count_values and array_intersect to obtain the array(s) you want.

The first one is used to know which values do exist in your array (and counts them so it's easy to filter out every non-duplicate one), and the second function does preserve the keys. If you know the duplicated value upfront, you only need to use the latter:

$duplicatesArray = array_intersect($array, array($duplicate));

Full example:

/**
 * @param array $array
 * @param int $threshold (optional) minimum number of elements per group
 * @return array
 */
function array_group_by_value(array $array, $threshold = 1)
{
    $grouped = array();
    foreach(array_count_values($array) as $value => $count)
    {
        if ($count < $threshold) continue;
        $grouped[$value] = array_intersect($array, array($value));
    }
    return $grouped;
}

Usage Example:

$test = array('a', 'b', 'a', 'a', 'b', 'c');

var_dump(array_group_by_value($test, 2));

Output:

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

Nenad Vukicevic · Accepted Answer · 2012-05-03 14:01:33Z

1

If you need all duplicates in one array, You can try:

$unique = array_unique($array); //get unique values
$diff = array_diff_assoc($array, $unique); //get duplicates
$intersect = array_intersect($unique, $diff); //get unique values with duplicates
return $intersect+$diff; //join unique with duplicates and duplicates

answered May 3, 2012 at 14:01

Nenad Vukicevic

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Comments

Sebastian Breit · Accepted Answer · 2012-05-03 13:20:14Z

0

$duplicated=null;

foreach($yourarray as $k => $v){
    foreach($yourarray as $k2 => $v2){
        if($v == $v2 && $k2 != $k){
            $duplicated[$k]=$v;
        }
    }
}

answered May 3, 2012 at 13:20

Sebastian Breit

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1 Comment

mickmackusa Over a year ago

I don't think I recommend this answer (versus other answers) because it is always making n x n conditional checks with the nested loop. I mean, the same outcome is achieved with fewer iterations by implementing a break. 3v4l.org/Doo0R I'll admit that I haven't thought too deeply about this task, but array_count_values() feels like a direct way of identifying duplicates without re-searching the input array over and over.

Rohit Choudhary · Accepted Answer · 2012-05-03 13:18:35Z

-1

You can use array_unique().http://php.net/manual/en/function.array-unique.php

answered May 3, 2012 at 13:18

Rohit Choudhary

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1 Comment

danneth Over a year ago

Judging by the question, this is the opposite. OP is asking to KEEP the duplicates, not remove them

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