group array of php objects by object property

Question

I have a php object (book) with 3 properties: name, category, description I then have a list of these book objects in an array. I want to create a new associative array for these objects grouped by category.

Say I have 4 book objects in an array called $books

name    category  description
==================================
book1   cat1     this is book 1
book2   cat1     this is book 2
book3   cat2     this is book 3
book4   cat3     this is book 4

how can I create an associative array called $categories

$categories['cat1'] = array(book1, book2)
$categories['cat2'] = array(book2)
$categories['cat3'] = array(book3)

where book? is the book object and not the word

Akarun · Accepted Answer · 2011-03-10 18:10:46Z

64

Like this:

foreach($books as $book)
{ 
    $categories[$book->category][] = $book;
}

answered Mar 10, 2011 at 18:10

Akarun

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2 Comments

Travis Hohl Over a year ago

If you've found this answer and aren't immediately aware of what it's doing -- it's creating a new array (named $categories) with a key for every value of $book->category. Each key's value is an array of $book objects that correspond to that $book->category. I'd make an ASCII picture if it wouldn't look like mud in this comment.

Travis Hohl Over a year ago

And if you want to sort the categories, that's extra: ksort($categories); See php.net/manual/en/function.ksort.php

RobertPitt · Accepted Answer · 2011-03-10 18:11:05Z

Simply loop the array of objects into a new array with the key being the category:

$newArray = array();
foreach($array as $entity)
{
    if(!isset($newArray[$entity->category]))
    {
         $newArray[$entity->category] = array();
    }

    $newArray[$entity->category][] = $entity;
}

Is this what you was looking for ?

Explanation of the code:

/*
    * Create a new blank array, to store the organized data in.
*/
$newArray = array();

/*
    * Start looping your original dataset
*/
foreach($array as $entity)
{

    /*
        * If the key in the new array does not exists, set it to a blank array.
    */
    if(!isset($newArray[$entity->category]))
    {
         $newArray[$entity->category] = array();
    }

    /*
        * Add a new item to the array, making shore it falls into the correct category / key
    */
    $newArray[$entity->category][] = $entity;
}

woru · Accepted Answer · 2015-01-07 21:51:12Z

4

You can do it with ouzo goodies:

 $categories = Arrays::groupBy($books, Functions::extractField('category'));

See: http://ouzo.readthedocs.org/en/latest/utils/arrays.html#groupby

answered Jan 7, 2015 at 21:51

woru

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Comments

Piotr Salaciak · Accepted Answer · 2011-03-10 18:10:40Z

1

$categories = array();

for ($i = 0; $i < count($books); $i++){
    if (isset($categories[$books[$i]->category]) == false)
        $categories[$books[$i]->category] = array();

    $categories[$books[$i]->category][] = $books[$i]
}

cheers

answered Mar 10, 2011 at 18:10

Piotr Salaciak

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Comments

linepogl · Accepted Answer · 2011-03-10 18:11:24Z

0

Try this:

$categories = array();
foreach ($books as $book){

  if (!array_key_exists($book->category , $categories))
     $categories[$book->category] = array();

  $categories[$book->category][] = $book;

}

answered Mar 10, 2011 at 18:11

linepogl

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Comments

Francesco Terenzani · Accepted Answer · 2011-03-10 18:12:52Z

0

This should works:

$categories = array();
foreach ($books as $book) {

    $categories[$book['category']][] = $book;

}

answered Mar 10, 2011 at 18:12

Francesco Terenzani

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1 Comment

rink.attendant.6 Over a year ago

Unlike JavaScript, you cannot access object properties with the array [propertyName] syntax.

jake · Accepted Answer · 2016-03-13 11:05:51Z

0

I had a similar problem, but a bit more complicated with wordpress and metavalues/metakeys (where $results was an array of associative arrays fetched from a $wpdb->get_results() query.

This was my solution adapted to your problem:

$categories = array();
foreach ($results as $row) {
    $id =  $row['category'];
    $description = $row['category'];
    $name = $row['name']
    if (!isset($categories[$id])) {
        $categories[$id] = array();
    }
    $categories[$id] = array_merge($categories[$id], 'description'=>$description , 'name'=>$name);
}

Then you can run another for loop to get each array from the categories array:

foreach ($categories as $category) {
    var_dump($category);
}

answered Mar 13, 2016 at 11:05

jake

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Comments

Minwork · Accepted Answer · 2018-09-06 09:33:50Z

0

If you want to group objects by getting key from specific method with or without additional arguments, you can use this library method:

Arr::groupObjects(array $objects, string $method, ...$args): array

answered Sep 6, 2018 at 9:33

Minwork

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