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On the Use of the array_walk_recursive( ) Function

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BACKGROUND:  The following routine takes a nested, associative array whose end-values are empty, extracts the keys of each non-recursive subarray, and properly echoes each.  Rather, than returning the result as a newly constituted array, however, the function returns boolean true and displays the desired result in a non-useable form.

Now, I have tried in vain to get the call-back function to produce an index-array of the echoed values that I can use outside the scope of the array_walk_recursive( ) function, but have failed miserably.

QUESTION:  How does one produce from the function a useable array that can be used outside of the function.

$result = array_walk_recursive($insertion_vars, function($key, $value) {
	echo $value . '<br />';
});

 

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How exactly do you want the resulting array structure to look?

In the callback, the first parameter is actually the value, the second parameter is the key. If you want to manipulate the existing array, make the parameter a reference using &. Any changes made to it will reflect in the array.

This example prefixes all the array's values with "changed_":

array_walk_recursive($insertion_vars, function(&$item, $key) {
	$item = 'changed_' . $item;
});
print_r($insertion_vars);

 

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OK, you guys (Ingolme and Dsonesuk) pay attention!

Firstly and once again, the array called $insertion_vars is a nested associative array whose keys are well identified, but whose non-recursive endpoints (read values) are all empty.

Secondly, I wish to produce an indexed array whose values contain the keys of the key-value paris whose endpoints (read values) are empty.

Ingolme's suggestion changes the endpoint values from zero to 'changed_', it neither restructures the array, nor does it return the keys as values.  See code below:

Array (
	[subscriber] => changed_ 
	[time] => changed_
	[date] => changed_
	[letter] => Array (
		[letter_no] => changed_
		[letter_title] => changed_ 
		[letter_abstract] => changed_
		[letter_body] => changed_
		[letter_link] => changed_
		[Letter_links] => Array (
			[link_one] => changed_ 
			[link_two] => changed_
			[link_three] => changed_
			[link_four] => changed_
			[link_five] => changed_
			)
		)
	[student] => Array (
		[student_name] => changed_
		[student_bio] => changed_
		[student_img] => changed_
		)
	[qa] => Array (
		[question] => changed_
		[answer] => changed_
		)
	[podcast] => Array (
		[podcast_no] => changed_
		[podcast_title] => changed_ 
		[podcast_abstract] => changed_
		[podcast_itunes] => changed_
		)
	[nextletter] => Array (
		[nextletter_no] => changed_
		[nextletter_title] => changed_
		[nextletter_abstract] => changed_
		)
	[webmaster_updates] => Array (
		[new_features] => changed_
		[security] => changed_
		[upcoming_innovation] => changed_
		)
	[miscellany] => Array (
		[miscellany_one] => changed_
		[miscellany_two] => changed_
		[miscellany_three] => changed_
		)
	) 

Dsonesuk's suggestion, if I have understood it correctly, was already tried and leads to an empty array no different than the one defined outside of the function. Please see the code below:

$varnames = array();
$result = array_walk_recursive($insertion_vars, function($value, &$key) {
	$varnames[] = $key;
});
print_r($varnames); //  Array()

 

Edited by iwato

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My example was not a solution to your problem, but an example on how array_walk_recursive works. I don't just make code to copy and paste.

array_walk_recursive does not restructure an array, for that I'd suggest using loops, stacks or recursive functions.

In PHP you cannot access global variables from within a function without using the global keyword or the $GLOBALS array.

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Ingolme:  Alright, I am unable to restructure the input array of an array_walk_recursive function.  However, I know with certainty that I am able to echo the keys just as I would like them to appear as the values of an indexed array.  So, why can I not convert this ability into the desired array?

My logic being, if you can display it, you should be able to store it.

By the way declaring $varnames as a global variable either inside the callback function or outside of the array_walk_recursive( ) function in a callback function that is read into the array_walk_recursive( ) function fails.

 

Edited by iwato

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I tested for myself and this works just fine

$varnames = array();
$vars = array(
  'item1' => array(
    'value1' => 'a',
    'value2' => ''
  ),
  'item2' => array(
    'value3' => '',
    'value4' => 'b'
  )
);
$result = array_walk_recursive($vars, function($item, $key) {
  if(empty($item)) {
    $GLOBALS['varnames'][] = $key;
  }
});
print_r($varnames);

Displays:

Quote

Array ( [0] => value2 [1] => value3 )

 

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Yes, it works, even without the if-statement.  What I have learned from this exercise is that the $GLOBALS variable and the global keyword are not equivalent alternatives to achieving the same outcome.

Many thanks! And, still again.

Roddy

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$GLOBALS and global are both equivalent. Here's the same example using the global keyword:

$varnames = array();
$vars = array(
  'item1' => array(
    'value1' => 'a',
    'value2' => ''
  ),
  'item2' => array(
    'value3' => '',
    'value4' => 'b'
  )
);
$result = array_walk_recursive($vars, function($item, $key) {
  global $varnames;
  if(empty($item)) {
    $varnames[] = $key;
  }
});
print_r($varnames);

The if() statement is there because you asked for elements that had an empty value. If you don't put the if() statement then all keys will be displayed (Except those keys that contained an array)

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