Table of Contents
About Array Reduce
array_reduce is an array function that iteratively reduces an array to a single value by applying a callback function to elements in the array.
array_reduce(
array $array,
callable $callback,
mixed $initial = null
): mixed
It takes the following parameters:
- an array (what do we want to reduce),
- callback (the logic),
- initial value(for example, an empty array []).
Simple example:
Let's find unique values in array.
1. We have an array of products
// an array
$products = [
"shirt",
"shoes",
"shirt"
];
2. A callback function, which checks if an item is already in an array.
$reducer = function ($all, $item) {
if (!in_array($item, $all)) {
array_push($all, $item);
}
return $all;
};
- The variable
$itemholds the value of the current iteration of$products. - The variable
$allholds the return value of the previous iteration. Its initial value is defined as the last parameter inarray_reduce.
3. initial value
Since we return an array in the callback, the type must match the initial array (we define an empty array as the initial value).
$initial = [];
array_reduce()
$products = [
"shirt",
"shoes",
"shirt"
];
$reducer = function ($all, $item) {
if (!in_array($item, $all)) {
array_push($all, $item);
}
return $all;
};
$initial = [];
array_reduce($products, $reducer, $initial);
// this will return
// [
// "shirt",
// "shoes",
// ]
if we pass some initial values
array_reduce($products, $reducer, ["hat"]);
// this will return
// [
// "hat",
// "shirt",
// "shoes",
// ]
also, everything in one place:
array_reduce(
["shirt", "shoes", "shirt"], // an array to reduce
function ($all, $item) { // callback
if (!in_array($item, $all)) {
array_push($all, $item);
}
return $all;
},
[] // initial
);
Obviously, we can use array_unique($products) instead to achieve the same results in this example.
Practical example:
Let's say we have an array of products(key, value structure).
$products = [
["name" => "Product 1", "price" => 10],
["name" => "Product 1", "price" => 10],
["name" => "Product 1", "price" => 10],
["name" => "Product 2", "price" => 2],
["name" => "Product 3", "price" => 7],
["name" => "Product 2", "price" => 2],
];
And we need to create an array where we count the same products ($quantity) and sum their price ($total) like this:
[
"Product 1" => [
"total" => ...,
"quantity" => ...,
],
"Product 2" => [
"total" => ...,
"quantity" => ...,
],
...
]
we can use an array_reduce function:
array_reduce($products, $reducer, []);
where we pass $products and an empty array as initial value. all we need is to write the callback.
then, in the callback:
since
$itemis a key-value pair (["name" => "Product 1", "price" => 10]) for simplicity, we assign the name and its price to variables.We check if the item is in the array ($all):
- if there is one with the same key, we increase its quantity by 1 and add the price.
- if not, we push the item to $all and set its quantity to 1.
$products = [
["name" => "Product 1", "price" => 10],
["name" => "Product 1", "price" => 10],
["name" => "Product 1", "price" => 10],
["name" => "Product 2", "price" => 2],
["name" => "Product 3", "price" => 7],
["name" => "Product 2", "price" => 2],
];
$reducer = function ($all, $item) {
$name = $item["name"];
$price = $item["price"];
if (isset($all[$name])) {
$all[$name]["quantity"]++;
$all[$name]["total"] += $price;
} else {
$all[$name]["total"] = $price;
$all[$name]["quantity"] = 1;
}
return $all;
};
array_reduce($products, $reducer, []);
// and that will return:
// [
// "Product 1" => [
// "total" => 30,
// "quantity" => 3,
// ],
// "Product 2" => [
// "total" => 4,
// "quantity" => 2,
// ],
// "Product 3" => [
// "total" => 7,
// "quantity" => 1,
// ],
// ]
Try the code:
https://replit.com/@stafura/arrayreduce-in-PHP#main.php
Use cases:
There are many ways you can use the array_reduce function, such as:
- summing up all the elements of an array,
- flattening a nested array,
- grouping elements based on some criterion,
- counting the occurrences of items in an array,
- filtering an array based on some condition.
more info:
https://www.php.net/manual/en/function.array-reduce.php
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