group array of php objects by object property - php

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

Answer 1

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

Answer 2

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;
}

Answer 3

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

Answer 4

$categories = array();
for ($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

Answer 5

Try this:
$categories = array();
foreach ($books as $book){
if (!array_key_exists($book->category , $categories))
$categories[$book->category] = array();
$categories[$book->category][] = $book;
}

Answer 6

This should works:
$categories = array();
foreach ($books as $book) {
$categories[$book['category']][] = $book;
}

Answer 7

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);
}

Answer 8

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