Get unique value of one attribute from array of associative arrays

Question

I have an array like this:

$a = array(
    0 => array('type' => 'bar', 'image' => 'a.jpg'),
    1 => array('type' => 'food', 'image' => 'b.jpg'),
    2 => array('type' => 'bar', 'image' => 'c.jpg'),
    3 => array('type' => 'default', 'image' => 'd.jpg'),
    4 => array('type' => 'food', 'image' => 'e.jpg'),
    5 => array('type' => 'food', 'image' => 'f.jpg'),
    6 => array('type' => 'food', 'image' => 'h.jpg')
)

How do I figure out unique type values (which would be food, bar and default)? I could iterate through the array in a foreach loop but is there a better way doing it?

Feud

Answer 1

In PHP >= 5.3 with the use of anonymous functions:

$unique_types = array_unique(array_map(function($elem){return $elem['type'];}, $a));

For previous versions you can declare a separate function:

function get_type($elem)
{
    return $elem['type'];
}

$unique_types = array_unique(array_map("get_type", $a));

Debbradebby

Answer 2

Using PHP >= 5.5, you could do:

$ar = array_unique(array_column($a, 'type'));

print_r($ar):

Array ( 
    [0] => bar 
    [1] => food 
    [3] => default 
)

---

http://php.net/manual/en/function.array-column.php

http://php.net/manual/en/function.array-unique.php

Stob

Not sure why this has +5 upvotes, it is a clever solution, not very much straight forward. – Howsoever

@true How could this have been more straight forward? This looks like as simple as it gets. Using the updated functionalities available in newer versions of a language should be appreciated rather than getting confused about. – Go

For 1. Having to look up what the array_* do, what they return, if they modify the array by reference..etc. It is just a clever solution, not very much else to say here. Please don't take it personal. – Howsoever

So if someone has to look up why shouldn't they? It's like using mud buckets to cool water in 21st century just for the reason that I don't want to read power specifications of my Fridge that I just bought yesterday :) Plus even the OP mentioned they want are not looking for an old school method. – Go

And nope nothing personal, its just a small discussion about whether to use newer tools available in the newer versions of language, you're entitled to your opinion as much as anyone else is, so nothing wrong there :) – Go

@Mark M - Using language constructs rather than extensions would indicate you know the language .. foreach, isset are language constructs, array_* are extension functions that require implicit knmowledge – Howsoever

This is a neat solution but I'm using php 5.4, so can't really use this one. – Feud

Answer 3

An old fashioned way without using the fancy array_* functions. This way is simple and easy to understand. You aren't left wondering what is happening because it so straightforward.

$a = array(
    0 => array('type' => 'bar', 'image' => 'a.jpg'),
    1 => array('type' => 'food', 'image' => 'b.jpg'),
    2 => array('type' => 'bar', 'image' => 'c.jpg'),
    3 => array('type' => 'default', 'image' => 'd.jpg'),
    4 => array('type' => 'food', 'image' => 'e.jpg'),
    5 => array('type' => 'food', 'image' => 'f.jpg'),
    6 => array('type' => 'food', 'image' => 'h.jpg')
);

$types = array();

foreach($a as $key => $type) {
        if(! isset($types[$type['type']]))
                $types[$type['type']] = $type['type'];
}

var_dump($types);

Howsoever

Actually, one of the fastest answers due to any of array_* function provided does input array copying. Language constructs are better there. – Offstage

That is interesting that you mention language constructs, because I just posted a comment about language constructs in one of the other answers before I read your comment. – Howsoever

Answer 4

try this

$uniqueA = array_unique($a, "type");
// then to output the array just type
print_r($uniqueA);

Out

Answer 5

You could also use array_reduce.

This only doesn't work if the values of the attribute are an array or object, because those can't be set as the key of an array.

function array_unique_attr($arr, $key) {

    return array_keys( array_reduce($arr, function($newArr, $event) {

        $newArr[$key] = true;
        return $newArr;

    }, []) );

}

$unique_types = array_unique_attr($a, 'type');

Katherinkatherina