group array of php objects by object property

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开发者_如何学运维 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

Like this:

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

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;
}

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

$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

Try this:

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

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

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

}

This should works:

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

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

}

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);
}

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