How to Flatten a Multidimensional Array?

Question 1

Is it possible, in PHP, to flatten a (bi/multi)dimensional array without using recursion or references?

I'm only interested in the values so the keys can be ignored, I'm thinking in the lines of array_map() and array_values().

Question 2

You can use the Standard PHP Library (SPL) to "hide" the recursion.

$a = array(1,2,array(3,4, array(5,6,7), 8), 9);
$it = new RecursiveIteratorIterator(new RecursiveArrayIterator($a));
foreach($it as $v) {
  echo $v, " ";
}

prints

1 2 3 4 5 6 7 8 9

Question 3

Thanks for all the given answers.

I have transformed it in the following, which is an improved version. It eliminates the need of a root prefix, does not need to use references, it is cleaner to read, and it has a better name:

function array_flat($array, $prefix = '')
{
    $result = array();

    foreach ($array as $key => $value)
    {
        $new_key = $prefix . (empty($prefix) ? '' : '.') . $key;

        if (is_array($value))
        {
            $result = array_merge($result, array_flat($value, $new_key));
        }
        else
        {
            $result[$new_key] = $value;
        }
    }

    return $result;
}

Question 4

The variadiac php5.6+ version: (Offers the added benefits of not breaking on missing values and inserting null where values are missing.)

Code: (Demo)

var_export(array_map(function(){return implode(',',func_get_args());},...$text));

The non-variadic version:

Code: (Demo)

foreach($text as $i=>$v){
    $result[]=implode(',',array_column($text,$i));
}
var_export($result);

Input:

$text = [
    ['001','002','003'],
    ['America','Japan','South Korea'],
    ['Washington DC','Tokyo','Seoul']
];

Output from either method:

array (
  0 => '001,America,Washington DC',
  1 => '002,Japan,Tokyo',
  2 => '003,South Korea,Seoul',
)

Nearly exact duplicate page: Combining array inside multidimensional array with same key

Question 5

Using List::Flatten seems like the easiest:

use List::Flatten;

my @foo = (1, 2, [3, 4, 5], 6, [7, 8], 9);        
my @bar = flat @foo;  # @bar contains 9 elements, same as (1 .. 9)

Actually, that module exports a single simple function flat, so you might as well copy the source code:

sub flat(@) {
    return map { ref eq 'ARRAY' ? @$_ : $_ } @_;
}

You could also make it recursive to support more than one level of flattening:

sub flat {  # no prototype for this one to avoid warnings
    return map { ref eq 'ARRAY' ? flat(@$_) : $_ } @_;
}

Question 6

You can do it like this, do the calculation from the innermost of the array. Check the demo.

<?php
function f(&$array)
{
    foreach($array as $k => &$v)
    {
        if(is_array($v))
        {
            if(count($v) == count($v, 1))
            {
                unset($array[$k]);
                if($k == 'sum')
                {
                    $v =  array_sum($v);
                    $array[] = $v;

                }elseif($k == 'multiply'){
                    $v = array_product($v);
                    $array[] = $v;
                }else{

                    foreach($v as $vv)
                        $array[] = $vv;
                }
            }else
                f($v);
        }
    }
}

while(count($array) != count($array, 1))
{
    f($array);
}

print_r($array);

Note：

traverse array from outer to inner
traverse array from inner to outer

How to Flatten a Multidimensional Array?

Answers

php,arrays,multidimensional-array,flatten