PHP Walk through multidimensional array while preserving keys

Question

I've got a multidimensional array of which I can't know the depth. The array could for example look like this:

$array = array(
    1 => array(
        5 => array(
            3 => 'testvalue1'
        )
    ),
    2 => array(
        6 => 'testvalue2'
    ),
    3 => 'testvalue3',
    4 => 'testvalue4',
);

With this array I want to create a table of contents. That means the keys need to be preserved as I'm using them as "chapter numbers". For example, "testvalue1" is in chapter 1.5.3.
Now I want to walk through the array while preserving all keys - not using array_walk_recursive as the keys containing another array are dropped (correct?) and preferably not using nested foreach loops considering the speed.
Any suggestions how I should do this? Thanks in advance.

PS: For my script it doesn't matter if the keys are strings ("1" instead of 1) or integers, if having strings as key will make array_walk_recursive preserve them.

@Gordon: Great answer, didn't know about RecursiveIteratorIterator :) Should come to good use. — Markus Hedlund
– Markus Hedlund, Commented Oct 21, 2011 at 20:33
RecursiveIteratorIterator seems to drop keys holding other arrays as well as array_walk_recursive.. Or am I wrong? — carlo
– carlo, Commented Oct 21, 2011 at 20:41

Community · Accepted Answer · 2017-05-23 11:53:52Z

9

You can iterate over your array with a help of a stack to build your toc.

$stack = &$array;
$separator = '.';
$toc = array();

while ($stack) {
    list($key, $value) = each($stack);
    unset($stack[$key]);
    if (is_array($value)) {
        $build = array($key => ''); # numbering without a title.
        foreach ($value as $subKey => $node)
            $build[$key . $separator . $subKey] = $node;
        $stack = $build + $stack;
        continue;
    }
    $toc[$key] = $key. ' ' . $value;
}

print_r($toc);

Output:

Array
(
    [1] => 1
    [1.5] => 1.5
    [1.5.3] => 1.5.3 testvalue1
    [2] => 2
    [2.6] => 2.6 testvalue2
    [3] => 3 testvalue3
    [4] => 4 testvalue4
)

You can additionally handle the level as well if you need to, but that was not clear from your question.

array_walk_recursive does not work, because it won't give you the keys of the parent element(s). See this related question as well: Transparently flatten an array, it has a good answer and is helpful for more generic cases as well.

edited May 23, 2017 at 11:53

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answered Oct 22, 2011 at 10:03

hakre

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3 Comments

carlo Over a year ago

There still is one problem; When the loop is one or more levels deeper into the array, it will only parse the first key / value and then returning to the first level of the array. For example, if you have $arr[1][0][1] and $arr[1][0][2], only $arr[1][0][1] will be parsed and then the loop will continue with $arr[2]... and soforth.. How can this be solved?

hakre Over a year ago

@Carlo: Didn't see you noticed that here. I edited the code to not have the issue. The array_shift function did re-number your array(s) as you are using integer-numeric keys, that is a specialty with PHP's arrays. If you do not need the numbers w/o a title, I've left a comment where they are added.

jazkat Over a year ago

Perfect. Only I wanted $toc to be string, so I replaced $toc = array(); with $toc = ''; and replaced the line $toc[$key] = $key. ' ' . $value; with $toc .= '['.$key. ']' . $value . ' - ';

hakre · Accepted Answer · 2011-10-22 10:24:21Z

2

<?php
    $td = array(1=>array(5=>array(3=>'testvalue1',array(6=>'testvalue2'))),2=>array(6=>'testvalue2',array(6=>'testvalue2',array(6=>'testvalue2'),array(6=>'testvalue2',array(6=>'testvalue2')))),3=>'testvalue3',4=>'testvalue4');
    print_r($td);
    $toc = '';

    function TOC($arr,$ke='',$l=array()) {
            if (is_array($arr)) {
            if ($ke != '') array_push($l,$ke);
            foreach($arr as $k => $v)
                TOC($v,$k,$l);
        }
        else {
            array_push($l,$ke);
            $GLOBALS['toc'].=implode('.',$l)." = $arr\n";
        }
    }
    toc($td);
    echo "\n\n".$toc;
?>

http://codepad.org/4l4385MZ

edited Oct 22, 2011 at 10:24

hakre

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answered Oct 21, 2011 at 20:37

Korvin Szanto

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4 Comments

carlo Over a year ago

Isn't there any other way not having to use many nested loops? Thanks anyway :)

Korvin Szanto Over a year ago

You must nest loops to iterate multidimensional arrays.

Markus Hedlund Over a year ago

@carlo Recursion is really the easiest solution for this problem.

hakre Over a year ago

@Korvin Szanto: You do not must nest loops, you can. See stackoverflow.com/questions/7854940/…

Kevin Vandenborne · Accepted Answer · 2011-10-21 21:50:55Z

Try this:

<?php
$ar = array(
    1 => array(
        5 => array(
            3 => 'testvalue1',
            5 => 'test',
            6 => array(
                9 => 'testval 9'
            )
        ),
        8 => 'testvalue9'
    ),
    2 => array(
        6 => 'testvalue2',
        7 => 'testvalue8',
        2 => array(
            6 => 'testvalue2',
            7 => 'testvalue8'
        ),
    ),
    3 => 'testvalue3',
    4 => 'testvalue4'
);

function getNestedItems($input, $level = array()){
    $output = array();

    foreach($input as $key => $item){
        $level[] = $key;
        if(is_array($item)){
            $output = (array)$output + (array)getNestedItems($item, $level);
        } else {
            $output[(string)implode('.', $level)] = $item;
        }
        array_pop($level);
     }
     return $output;
}

var_dump(getNestedItems($ar));

Kevinleary.net · Accepted Answer · 2024-04-10 14:14:46Z

0

Another take on this that worked best for me with handling deep nested multidimensional associative and non-associative arrays:

/**
 * Flatten a Multidimensional Array
 */
function array_multidimensional_flatten( $array, $position = [], $separator = '.' ) {
  if ( !is_array( $array ) ) {
    return false;
  }

  $result = [];

  foreach ( $array as $key => $value ) {
    if ( is_array( $value ) ) {
      $position[] = $key;
      $result = array_merge( $result, array_multidimensional_flatten( $value, $position ) );
    } else {
      if ( $position ) {
        $key = implode( $separator, $position ) . "{$separator}{$key}";
      }
      $result = array_merge( $result, [$key => $value] );
    }
  }

  return $result;
}

Using it with a large multidimensional array will output something like this:

[
  'hero__overlay-opacity' => '100',
  'hero__lead-in' => 'Underwritten by TruStage® Insurance',
  'hero__optimize' => '1',
  'hero__layout' => 'centered',
  'flexible-content.0.acf_fc_layout' => 'title',
  'flexible-content.0.acfe_flexible_toggle' => '',
  'flexible-content.0.text' => 'Enabling Smart Financial Decisions',
  'flexible-content.0.size.value' => 'lg',
  'flexible-content.0.size.label' => 'L',
  'flexible-content.0.size.alignment.value' => 'center',
  'flexible-content.0.size.alignment.label' => 'Center',
  'flexible-content.0.size.alignment.weight.value' => 'normal',
  'flexible-content.0.size.alignment.weight.label' => 'Regular',
  'flexible-content.0.1.acf_fc_layout' => 'grid-stats',
  'flexible-content.0.1.acfe_flexible_toggle' => '',
  'flexible-content.0.1.columns.0.statistic' => '85+',
  'flexible-content.0.1.columns.0.description' => 'Years of Experience',
  'flexible-content.0.1.columns.0.1.statistic' => 'A',
  'flexible-content.0.1.columns.0.1.description' => 'Financial rating1',
  'flexible-content.0.1.columns.0.1.2.statistic' => '4.75 / 5',
  'flexible-content.0.1.columns.0.1.2.description' => 'Rating on TrustPilot',
  'flexible-content.0.1.2.acf_fc_layout' => 'icon-columns',
  'flexible-content.0.1.2.acfe_flexible_toggle' => '',
  'flexible-content.0.1.2.title' => 'Insurance Products',
  'flexible-content.0.1.2.background' => 'rgb(246,246,246)',
  'flexible-content.0.1.2.alignment.value' => 'center',
  'flexible-content.0.1.2.alignment.label' => 'Center',
  'flexible-content.0.1.2.alignment.style.value' => 'default',
  'flexible-content.0.1.2.alignment.style.label' => 'Bordered Circle',
  'flexible-content.0.1.2.alignment.style.column.0.icon_type' => 'icon',
  'flexible-content.0.1.2.alignment.style.column.0.icon' => 'insurance-add',
  'flexible-content.0.1.2.alignment.style.column.0.image' => '',
  'flexible-content.0.1.2.alignment.style.column.0.title' => 'AD&D Insurance',
  'flexible-content.0.1.2.alignment.style.column.0.link' => '/insurance/accidental-death-dismemberment/',
]

answered Apr 10, 2024 at 14:14

Kevinleary.net

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3 Comments

mickmackusa Over a year ago

I do not support the conditional return of false. PHP doesn't have a false coalescing operator. If you are going to conditionally return a non-array, then use null (or even better throw an exception). These options will allow you to declare the return type as array (or slightly worse ?array). I recommend type declarations on the first parameter array $array anyhow.

mickmackusa Over a year ago

Instead of if ( $position ) {$key = implode( $separator, $position ) . "{$separator}{$key}";}, I might suggest unconditionally writing: $key = implode($separator, array_merge($position, $key)); for brevity. If you still want the condition, you can still wrap that in a if ($position) check.

mickmackusa Over a year ago

$result = array_merge( $result, [$key => $value] ); can be simplified to $result[$key] = $value];

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