How to change the value of an element with array_walk?

Question

How can I change the value of an element with array_walk?

For instance, this is my array,

$items = array(
    0 => array( 
        "id" => "1",
        "title" => "parent 1",
       "children" => array()
        ),

    1 => array( 
        "id" => "2",
        "title" => "parent 2",
        "children" => array (
           0 => array( 
            "id" => "4",
            "title" => "children 1"
            ),
           1 => array( 
            "id" => "5",
            "title" => "children 2"
            ) 
        ),
   )
);

And I can change it with this below,

function myfunction(&$item,$key)
{
    if($item['id'] === '1')
    {
        $item['title'] = 'hello world en';
    }   
}


array_walk($items,"myfunction");

print_r($items);

But I have a nested children and I want to change the value in that too, and I will get error if I do this,

function myfunction(&$item,$key)
{
    if($item['id'] === '1')
    {
        $item['title'] = 'hello world en';
    }

    if($item['id'] === '4')
    {
        $item['title'] = 'hello world en';
    }


    foreach($item as $key => $value)
    {

        if(is_array($value))
        {
            myfunction($value,$key);
        }
    }

}

error,

Notice: Undefined index: id in ...index.php on line xx

Any idea what should I do if there is a nested children in an array?

In first place you should not have $arr['hardcodedKeyName'] before any check is done. You cannot be sure this key is present or not. You should recursively get through the last depth of array searching for id and change if present, then go to the beginning — Ivan Yonkov
– Ivan Yonkov, Commented Jul 15, 2014 at 13:21

Alma Do · Accepted Answer · 2014-07-15 13:27:54Z

8

You may achieve that with recursive call of your callback function. I've implemented sample with closure, like:

//replacement array:
$replace = [
  '1' => 'foo',
  '2' => 'bar',
  '5' => 'baz'
];

array_walk($items, $f=function(&$value, $key) use (&$f, $replace)
{
   if(isset($replace[$value['id']]))
   {
      $value['title'] = $replace[$value['id']];
   }
   if(isset($value['children']))
   {
      //the loop which is failing in question:
      foreach($value['children'] as $k=>&$child)
      {
         $f($child, $k);
      }
      //Proper usage would be - to take advantage of $f
      //array_walk($value['children'], $f);
   }
});

As you can see - all that you need is to pass value by reference and iterate it inside callback as a reference for foreach too.

edited Jul 15, 2014 at 13:27

answered Jul 15, 2014 at 13:22

Alma Do

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1 Comment

hyperplural Over a year ago

Interesting recursive solution.

kero · Accepted Answer · 2014-07-15 13:20:40Z

2

When you add a line such as if (!isSet($item['id'])) var_dump($item); you will see why you get the undefined index.

Although I am not sure why you're doing this (how are you taking advantage of array_walk()?), to solve this, you could use something like the following:

function myfunction(&$item,$key)
{
    if ($item['id'] === '1')
    {
        $item['title'] = 'hello world en';
    }

    if ($item['id'] === '4')
    {
        $item['title'] = 'hello world en';
    }


    if (isSet($item['children']) && is_array($item['children']))
        array_walk($item['children'], __FUNCTION__);
}

Which will work with the example given.

answered Jul 15, 2014 at 13:20

kero

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Comments

Daniel K. · Accepted Answer · 2014-07-15 13:21:55Z

1

foreach($item as $key => $value)
{

    if(is_array($value))
    {
        myfunction($value,$key);
    }
}

You walk through every key in your $item (id, title, children). But I guess what you want is moving through every ELEMENT of $value['children'] (value['children'][0], value['children'][1]), right? So it might be something like this:

if(is_array($value)){
   foreach($item['children'] as $key => $value){
      myfunction($value,$key);
   }
}

answered Jul 15, 2014 at 13:21

Daniel K.

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Comments

Styphon · Accepted Answer · 2014-07-15 13:24:59Z

The problem is you're passing in your whole array of children, not each individual item of children. See this eval for how it should look. And here's the code:

<?php
$items = array(
    0 => array( 
        "id" => "1",
        "title" => "parent 1",
        "children" => array()
    ),

    1 => array( 
        "id" => "2",
        "title" => "parent 2",
        "children" => array (
           0 => array( 
            "id" => "4",
            "title" => "children 1"
            ),
           1 => array( 
            "id" => "5",
            "title" => "children 2"
            ) 
        ),
   )
);

function myfunction(&$item) {
  if($item['id'] == '1' || $item['id'] == '4') {
    $item['title'] = 'hello world en';
  }
  if( ! empty($item['children'])) {
    array_walk($item['children'], "myfunction");
  }
}

array_walk($items, "myfunction");

var_dump($items);

hlscalon · Accepted Answer · 2014-07-15 13:54:19Z

-1

In the code you posted you are not passing the reference through foreach. This should work with the code you posted.

foreach($item as $key => &$value)
{
    if(is_array($value)) {
        myfunction($value,$key);
    }
}

And to you don't see the undefined index, just check if that is setted before comparing the values:

if(isset($item['id'])){
    if($item['id'] === '1'){
      ...
    }
}

Online example

edited Jul 15, 2014 at 13:54

answered Jul 15, 2014 at 13:23

hlscalon

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5 Comments

Ivan Yonkov Over a year ago

Not sure it's relevant

hlscalon Over a year ago

@RoyalBg well, I just tested online and worked. Ill update to add the link

Ivan Yonkov Over a year ago

The errors for undefined indices are still present, you saw?

PHP Notice:  Undefined index: id in /home/v5qmCF/prog.php on line 28 PHP Notice:  Undefined index: id in /home/v5qmCF/prog.php on line 33 PHP Notice:  Undefined index: id in /home/v5qmCF/prog.php on line 28 PHP Notice:  Undefined index: id in /home/v5qmCF/prog.php on line 33

hlscalon Over a year ago

@RoyalBg Yes, of course there are better ways of doing this, and I didn't correct all errors, etc. Im just saying why his code is not updating the values in deep levels.

Ivan Yonkov Over a year ago

A part of the main question was about the undefined index error

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