How to create a recursive function to unset multidimentional array in PHP?

Question

Below is my target array which I would like to unset its elements by key based on the candidate array element.

$target = [
    60 => "Home"
    "Villa" => [
        "30" => "Vi",
    ],
    70 => "A",
    40 => "B",
    50 => "C",
    "Land" => [
        1 => "La",
        35 => "Lb",
        37 => "Lc",
        39 => "Ld",
    ],
];

$candidate = [30, 50, 35, 37];

Below is the result that I want after unsetting.

$target = [
    60 => "Home"
    70 => "A",
    40 => "B",
    "Land" => [
        1 => "La",
        39 => "Ld",
    ],
];

'Villa' must also be gone because it's empty after it's element "30" => "Vi" has been unset.

Below my solution in for-loop.

foreach ($target as $id => $option) {
    if (isset($candidate[$id])) {
      unset($target[$id]);
    }
    elseif (is_array($option)) {
      foreach ($option as $sub_id => $opt) {
        if (isset($candidate[$sub_id])) {
          unset($target[$id][$sub_id]);
        }
      }
    }

    if (!count($target[$id])) {
      unset($target[$id]);
    }
}

How can I replace this for-loop in a recursive solution?

My multidimensional array might go deeper than this in the future. — O Connor
– O Connor, Commented Jan 12, 2018 at 15:25
Why are you not unsetting the whole array with unset($target)? — Ananta
– Ananta, Commented Jan 12, 2018 at 15:30
Then I will get empty $target as result? I only want to unset the elements based on the $candidate array. — O Connor
– O Connor, Commented Jan 12, 2018 at 15:31

Vladimir · Accepted Answer · 2018-01-12 15:42:46Z

3

function del($target, $candidate) {
    foreach ($target as $key => $value) {
        if (in_array($key, $candidate)) {
            unset($target[$key]);
        } elseif (is_array($value)) {
            $target[$key] = del($value, $candidate);
            if (!count($target[$key])) {
                unset($target[$key]);
            }
        }
    }
    return $target;
}

$new = del($target, $candidate);
var_dump($new);

answered Jan 12, 2018 at 15:42

Vladimir

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Comments

symcbean · Accepted Answer · 2018-01-12 16:05:20Z

3

This started as a comment on Mehdi's answer, but I ran out of space:

While I believe arrays are passed by reference, and there should be minimal overhead assigning the reference to the variable it came from, it strikes me that explicitly passing by reference might be more robust and transparent.

i.e.

function clean(&$target, $candidate, $depth=0){
   if (++$depth>10) {
      // erk!
      trigger_error("Too deep!");
   }
   // Loop through candidates
   foreach($candidate as $index){
       // If the value is an array
       if(isset($target[$index]) && is_array($target[$index])){
           clean($target[$index], $candidate, $depth);
           if (!count($target[$index])) unset($target[$index]); // thanks jhilgeman
       } else {
           isset($target[$index]) && unset($target[$index]);
       }
   }
}

clean($target, $candidate);
var_dump($target);

edited Jan 12, 2018 at 16:05

answered Jan 12, 2018 at 15:44

symcbean

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5 Comments

Spoody Over a year ago

It is actually, I updated my code with reference and unsetting empty arrays, but here I'm staring at my computer frozen.

jhilgeman Over a year ago

Sadly I wasn't able to get to my desk before someone answered this one, but this is what I would have written (using pass-by-reference). One thing that you need to also add is after the clean() line, check to see if $target[$index] is now empty and unset it if so. This addresses the requirement about "'Villa' must also be gone because it's empty after...". Example code to add: if(!count($target[$index])) { unset($target[$index]); }

symcbean Over a year ago

Have a +1 for the empty array fix then :)

symcbean Over a year ago

(there was also a bug - my code wasn't checking if the index was in $candidate before deleting!)

symcbean Over a year ago

...and since we should be exempliying good programming practice, I've added a limit on the recursion

Spoody · Accepted Answer · 2018-01-14 15:07:29Z

1

EDIT:

<?php
$target = [
    60 => "Home",
    "Villa" => [
        "30" => "Vi",
    ],
    70 => "A",
    40 => "B",
    50 => "C",
    "Land" => [
        1 => "La",
        35 => "Lb",
        37 => "Lc",
        39 => "Ld",
    ],
];

$candidate = [30, 50, 35, 37];

function clean(&$target, $candidate){
    // Loop through target
    foreach($target as $index => $value){
        // If the value is an array
        if(is_array($value)){
            // Clean it first
            $result = clean($value, $candidate);
            $target[$index] = $result;
        } else {
            // Check if the key is in the candidate array
            if(in_array($index, $candidate)){
                $target[$index] = NULL;
            }
        }
        // If the value is empty
        if(empty($target[$index])){
            // Unset it
            unset($target[$index]);
        }
    }
}

$target = clean($target, $candidate);

var_dump($target);

Result:

/var/www/test.php:47:
array (size=4)
  60 => string 'Home' (length=4)
  70 => string 'A' (length=1)
  40 => string 'B' (length=1)
  'Land' => 
    array (size=2)
      1 => string 'La' (length=2)
      39 => string 'Ld' (length=2)

As symcbean mentioned using reference here would be better

edited Jan 14, 2018 at 15:07

answered Jan 12, 2018 at 15:34

Spoody

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2 Comments

O Connor Over a year ago

what does it mean "Using reference"?

Spoody Over a year ago

I meant instead of copying the variable to the function you can just pass a reference to the variable you want to work with (I should've removed the return part from the function)

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