Recursively group arrays on multiple keys - php

Question

I have an array of objects for example:
Array
(
[0] => Array
(
[Id] => 1
[Name] => Toy Car
[Category] => Toys
[Price] => 2.99
[OnSale] => false
)
...
)
But I'd like them to be grouped by Category, then by OnSale.
So far I have been able to group by category using:
$result = array();
foreach ($data as $element) {
$result[$element['Category']][] = $element;
}
But I am unsure how to nest another foreach or recursively group them once they have been grouped by Category. Any help is appreciated!

Answer 1

Do you mean:
$result = array();
foreach ($data as $element) {
$result[$element['Category']][$element['OnSale']][] = $element;
}
EDIT: Sorry, bit of a problem with all the [ and ]...

Answer 2

You're close! You just need to add the second key you want to group by.
$byCategoryAndSale = [];
foreach ($inventory as $item) {
$byCategoryAndSale[$item['Category']][$item['OnSale']][] = $item;
}
Note Using a boolean value as an array key will equate to 1's and 0's which can get pretty confusing.
Here's a full example:
<?php
$inventory = [
[
'Id' => 1,
'Name' => 'Toy Car',
'Category' => 'Toys',
'Price' => 2.99,
'OnSale' => false
],
[
'Id' => 2,
'Name' => 'Another Toy',
'Category' => 'Toys',
'Price' => 1.99,
'OnSale' => false
],
[
'Id' => 3,
'Name' => 'Hamburger',
'Category' => 'Not Toys',
'Price' => 5.99,
'OnSale' => false
],
[
'Id' => 4,
'Name' => 'Last Toy',
'Category' => 'Toys',
'Price' => 50.99,
'OnSale' => true
]
];
$byCategoryAndSale = [];
foreach ($inventory as $item) {
$byCategoryAndSale[$item['Category']][$item['OnSale']][] = $item;
}
print_r($byCategoryAndSale);
?>
Which yields:
PS C:\> php test.php
(
[Toys] => Array
(
[0] => Array
(
[0] => Array
(
[Id] => 1
[Name] => Toy Car
[Category] => Toys
[Price] => 2.99
[OnSale] =>
)
[1] => Array
(
[Id] => 2
[Name] => Another Toy
[Category] => Toys
[Price] => 1.99
[OnSale] =>
)
)
[1] => Array
(
[0] => Array
(
[Id] => 4
[Name] => Last Toy
[Category] => Toys
[Price] => 50.99
[OnSale] => 1
)
)
)
[Not Toys] => Array
(
[0] => Array
(
[0] => Array
(
[Id] => 3
[Name] => Hamburger
[Category] => Not Toys
[Price] => 5.99
[OnSale] =>
)
)
)
)