How to get unique values from one column of a 2d array

Question

I have a placeholder array called $holder, values as follows:

Array ( [0] => Array ( [id] => 1 [pid] => 121 [uuid] => 1 ) [1] => Array ( [id] => 2 [pid] => 13 [uuid] => 1 ) [2] => Array ( [id] => 5 [pid] => 121 [uuid] => 1 ) )

I am trying to pull out distinct/unique values from this multidimensional array. The end result I would like is either a variable containing (13,121), or (preferrably) an array as follows: Array( [0] => 13 [1] => 121 )

Again I've tried serializing and such, but don't quite understand how that works when operating with a single key in each array.

possible duplicate PHP remove duplicate values from multidimensional array — arun
– arun, Commented May 2, 2012 at 6:09

deceze · Accepted Answer · 2012-05-02 06:06:22Z

75

Seems pretty simple: extract all pid values into their own array, run it through array_unique:

$uniquePids = array_unique(array_map(function ($i) { return $i['pid']; }, $holder));

The same thing in longhand:

$pids = array(); foreach ($holder as $h) { $pids[] = $h['pid']; } $uniquePids = array_unique($pids);

answered May 2, 2012 at 6:06

deceze♦

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4 Comments

Ilia Ross Over a year ago

I wonder why this doesn't work array_unique(array_map(function ($i) { return $i[$id]; }, $holder)); Is there a way to use variable instead of predefined key name?

Ilia Ross Over a year ago

@deceze Ah, alright, it's inside of anonymous function. Thanks!

Jorge Orpinel Pérez Over a year ago

This works but is inefficient. Why add a bunch of elements and remove them immediately? Just loop over the array and filter one by one! I'm adding my own answer.

deceze Over a year ago

@Jorge Yes, this could be made more efficient by looping over the array once, putting all its elements into a new array as keys, then extracting just the keys. However, there's a tradeoff between readability, maintainability and performance, and I think this solution strikes a decent balance which will be just fine for average sized arrays.

Dondi Imperial · Accepted Answer · 2015-05-25 14:48:25Z

42

In php >= 5.5 you can use array_column:

array_unique(array_column($holder, 'pid'));

answered May 25, 2015 at 14:48

Dondi Imperial

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Comments

Nauphal · Accepted Answer · 2012-05-02 06:08:11Z

try this

foreach($arr as $key => $val) { $new_arr[] = $val['pid']; } $uniq_arr = array_unique($new_arr);

konsolenfreddy · Accepted Answer · 2012-05-02 06:08:24Z

Just iterate over it and apply an array_unique on the result:

foreach($holder as $yourValues){ $pids[] = $yourValues['pid']; } $yourUniquePids = array_unique($pids);

Jorge Orpinel Pérez · Accepted Answer · 2015-02-11 23:43:30Z

Assuming your array is called $holder:

$unique = array(); foreach( $holder as $h ) if( ! in_array($h, $unique ) ) $unique[] = $h;

is a slightly more efficient way than via array_unique, I believe. May be the same.

in_array is essentially looping over the array again and again, so you've got two nested loops. That's inefficient in its own way.

Anti logic · Accepted Answer · 2020-02-03 13:25:37Z

$uniquearray = []; for($i=0;$i<count($assocarray);$i++){ if(!in_array($assocarray[$i]['KEY'],$uniquearray)){ $uniquearray[$i]= $assocarray[$i]['KEY']; } }

Can you provide a brief explanation in addition to your code?

Er. Anurag Jain · Accepted Answer · 2012-05-02 06:30:04Z

Hi Please try code given below for get unique values and then sort that values

<?php $sort_arr = unique_sort($holder, 'pid'); echo "<pre>"; print_r($sort_arr); echo"</pre>"; /*function for get unique value then sort them*/ function unique_sort($arrs, $id) { $unique_arr = array(); foreach ($arrs AS $arr) { if (!in_array($arr[$id], $unique_arr)) { $unique_arr[] = $arr[$id]; } } sort($unique_arr); return $unique_arr; }

thanks

mickmackusa · Accepted Answer · 2025-08-30 22:34:54Z

Because your identical values are probably integers (they can be safely used as array keys with risk of corruption/truncation), you can avoid calling array_unique() if you duplicate the second parameter of array_column() as the third parameter.

$uniqueness = array_column($array, 'id', 'id'); // [13 => 13, 121 => 121]

If your subsequent processing ignores keys, then you don't need to reindex the array.

azwart · Accepted Answer · 2016-12-30 09:11:45Z

fo my situation i use this method

//get some data from db to array while ($row = mysqli_fetch_assoc($query)){ $data[] = $row; } //display unique value echo "<table>"; $uniq = array(); foreach ($data as $row) { if(!in_array($row['path'], $uniq)) { $uniq[] = $row['path']; echo "<tr>"; echo "<td>"; echo $row['path']; echo "</td>"; echo "<td>"; echo $row['relationship_id']; echo "</td>"; echo "</tr>"; } } echo "</table>";

I don't see how that respond to the question: wich is getting unique value in a multidimensional array

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