Php make array flat

How to Flatten an array in PHP (four methods)

There’s no built-in operate in PHP to flatten a multi-dimensional array, however it’s not a tough factor to do in PHP. In reality, it’s fairly straightforward.

We normally flatten arrays of information fetched from a database or an API. In real-world eventualities, we’d normally wish to take a number of fields off every row for displaying in our views.

Easy methods to flatten an array in PHP

On this tutorial, we’ll discover 4 methods of flattening arrays (two-dimensional and multi-dimensional) in PHP:

1. Flatten two-dimensional arrays in PHP (when keys don’t matter)
2. Pluck a listing of the given key/worth pairs from a PHP array
3. Flatten a PHP array recursively I
4. Flatten a PHP array recursively II

Flatten two-dimensional arrays in PHP

If in case you have a two-dimensional array, you’ll be able to flatten it by unpacking the array and passing it as an argument to the array_merge() operate.

 // Every array has two Apple units in every class (iPads, telephones, and laptops) $merchandise = [ ['iPad Air', 'iPad pro'], ['iPhone 13', 'iPhone 13 mini'], ['MacBook Air', 'MacBook Pro'] ]; // Flatten the array $end result = array_merge(. $merchandise); print_r($end result); 

And this would be the output:

Array ( [0] => iPad Air [1] => iPad professional [2] => iPhone 13 [3] => iPhone 13 mini [4] => MacBook Air [5] => MacBook Professional ) 

In PHP variations earlier than 8.1, if the $merchandise array has string keys, you could extract the values with array_values() first:

 // . $end result = array_merge(. array_values($merchandise)); 

For PHP variations earlier than 7.4: if the $merchandise array is empty, the array_merge() can be invoked with out arguments. This may elevate an error. To keep away from the error, add an empty array [] to the array_merge() arguments:

 // . $outcomes = array_merge([], . $merchandise); 

Argument unpacking has been accessible since PHP 5.6+.

Be aware: Since PHP 8.1, unpacking the outer array with string keys (associative arrays) is feasible with out utilizing array_values() .

Pluck a listing of the given key/worth pairs from the array

If in case you have an array of arrays (two-dimensional), and also you wish to take a particular key (e.g., identify ) off every array and create an array of names, you need to use array_column() .

Think about you have fetched a listing of consumers from the database, and you’ve got the outcomes as a two-dimensional array. Now you wish to create an array containing the identify of every particular person.

Here is the way it’s achieved:

 // Array representing a potential report set returned from a database $data = array( array( 'id' => 2135, 'first_name' => 'John', 'last_name' => 'Doe', ), array( 'id' => 3245, 'first_name' => 'Sally', 'last_name' => 'Smith', ), array( 'id' => 5342, 'first_name' => 'Jane', 'last_name' => 'Jones', ), array( 'id' => 5623, 'first_name' => 'Peter', 'last_name' => 'Doe', ) ); $first_names = array_column($data, 'first_name'); print_r($first_names); 

Array ( [0] => John [1] => Sally [2] => Jane [3] => Peter ) 

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Flattening arrays in PHP

To sum things up; if you want to flatten a two-dimensional array with numeric keys:

array_merge(. $twoDimensionalArray); 

If you want to flatten a two-dimensional associative array:

array_merge(. array_values($twoDimensionalArray)); 

If you want a general solution to flatten an arbitrarily nested array and you don’t care about the keys:

function flatten_array(array $array): array   $recursiveArrayIterator = new RecursiveArrayIterator(  $array,  RecursiveArrayIterator::CHILD_ARRAYS_ONLY  );  $iterator = new RecursiveIteratorIterator($recursiveArrayIterator);   return iterator_to_array($iterator, false); > 

If you want a general solution to flatten an arbitrarily nested array and you do care about the keys:

function flatten_array_preserve_keys(array $array): array   $recursiveArrayIterator = new RecursiveArrayIterator(  $array,  RecursiveArrayIterator::CHILD_ARRAYS_ONLY  );  $iterator = new RecursiveIteratorIterator($recursiveArrayIterator);   return iterator_to_array($iterator); > 

As a side note, if you are only interested in all values with a specific key 1 :

$array = [  ['id' => 123, 'name' => 'aaa', 'class' => 'x'],  ['id' => 124, 'name' => 'bbb', 'class' => 'x'],  ['id' => 345, 'name' => 'ccc', 'class' => 'y'], ];  array_column($array, 'id'); // [123, 124, 345] 

Flattening a two-dimensional array

array_merge(. $twoDimensionalArray); 

array_merge takes a variable list of arrays as arguments and merges them all into one array. By using the splat operator ( . ), every element of the two-dimensional array gets passed as an argument to array_merge .

This works fine for merging associative arrays as well, but beware that the outer array is only allowed to have numeric keys:

$twoDimensionalArray = [  'x' => ['first', 'array'],  'y' => ['second', 'array'] ];  $flattenedArray = array_merge(. $twoDimensionalArray); // Fatal error: Uncaught ArgumentCountError: array_merge() does not accept unknown named parameters 

The solution is to use array_values in those cases:

$twoDimensionalArray = [  'x' => ['first', 'array'],  'y' => ['second', 'array'] ];  $flattenedArray = array_merge(. array_values($twoDimensionalArray)); 

On PHP version 7.3 or lower, you will see the following if the input array is empty:

$twoDimensionalArray = []; array_merge(. $twoDimensionalArray); // Warning: array_merge() expects at least 1 parameter, 0 given. 

You can solve this by passing a single empty array as an extra argument:

array_merge([], . $twoDimensionalArray); 

A general solution for arbitrarily nested arrays

function flatten_array(array $array): array   $recursiveArrayIterator = new RecursiveArrayIterator(  $array,  RecursiveArrayIterator::CHILD_ARRAYS_ONLY  );  $iterator = new RecursiveIteratorIterator($recursiveArrayIterator);   return iterator_to_array($iterator, false); > 

For arbitrarily nested arrays we make use of the built-in iterators RecursiveArrayIterator and RecursiveIteratorIterator . It is important to note that we have to pass the flag CHILD_ARRAYS_ONLY to the ArrayIterator , otherwise it would iterate over public properties of objects as well, which you probably never want:

class Person   public function __construct(public $name) <> >  $array = [  new Person('Jake'),  new Person('Charles') ];  flatten_array($array); // Without CHILD_ARRAYS_ONLY: // // [ // 0 => 'Jake', // 1 => 'Charles' // ] // // With CHILD_ARRAYS_ONLY: // // [ // 0 => Person Object, // 1 => Person Object // ] 

Lastly, you can play around with the second argument of iterator_to_array , which indicates whether or not keys should be preserved. If you pass false , keys will not be preserved and the result will be a simple list. If you pass true (which is the default), keys will be preserved, meaning duplicate entries will be lost. Both approaches have their uses.

$employees = [  ['name' => 'Jake Peralta'],  ['name' => 'Charles Boyle'] ];  flatten_array($employees); // [ // 0 => 'Jake Peralta', // 1 => 'Charles Boyle, // ]  flatten_array_preserve_keys($employees); // [ // 'name' => 'Charles Boyle' // ] 

Extracting values with a specific key

array_column is especially useful to extract all values with a given key from an array:

$array = [  ['id' => 123, 'name' => 'aaa', 'class' => 'x'],  ['id' => 124, 'name' => 'bbb', 'class' => 'x'],  ['id' => 345, 'name' => 'ccc', 'class' => 'y'], ];  array_column($array, 'id'); // [123, 124, 345] 

The function accepts an optional third parameter that specifies which column to use as the index:

array_column($array, 'name', 'id'); // [123 => 'aaa', 124 => 'bbb', 345 => 'ccc'] 

It handles objects as well, as long as the properties are public:

class Person   public function __construct(public int $id, public string $name) <> >  $objects = [  new Person(12, 'John'),  new Person(34, 'Jane') ];  array_column($objects, 'name', 'id'); // [12 => 'John', 34 => 'Jane'] 

While not useful in the context of flattening arrays, there’s another neat trick you can do with array_column : by passing null as the second argument, the array will be reindexed based on the third parameter:

$array = [  ['id' => 123, 'name' => 'aaa', 'class' => 'x'],  ['id' => 124, 'name' => 'bbb', 'class' => 'x'],  ['id' => 345, 'name' => 'ccc', 'class' => 'y'], ];  array_column($array, null, 'id'); // [ // 123 => ['id' => 123, 'name' => 'aaa', 'class' => 'x'], // 124 => ['id' => 124, 'name' => 'bbb', 'class' => 'x'], // 345 => ['id' => 345, 'name' => 'ccc', 'class' => 'y'], // ] 

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