I got Undefined index: reading recursively an array - php

Question

I'm going to be crazy, I can't understand what is the problem.
I have this array:
array(2) {
[0]=>
array(4) {
["id"]=>
string(1) "1"
["parent_id"]=>
NULL
["name"]=>
string(7) "Events"
["children"]=>
array(2) {
[0]=>
array(3) {
["id"]=>
string(1) "2"
["parent_id"]=>
string(1) "1"
["name"]=>
string(9) "Concerts"
}
}
}
[1]=>
array(4) {
["id"]=>
string(1) "4"
["parent_id"]=>
NULL
["name"]=>
string(7) "Music"
["children"]=>
array(3) {
[0]=>
array(3) {
["id"]=>
string(1) "5"
["parent_id"]=>
string(1) "4"
["name"]=>
string(4) "Rock"
}
}
}
}
and I try to print with this recursive function:
public function printTree($tree) {
$result = "";
if(!is_null($tree) && count($tree) > 0) {
$result .= '<ul>';
foreach($tree as $node) {
$result .= '<li>Cat: '.$node['name'];
$subtree = array($node['children']);
$this->printTree($subtree);
$result .= '</li>';
}
$result .= '</ul>';
}
return $result;
}
I get an "Undefined index: name" error.
Do I need to declare name? how?
Is the array with incorrect syntax?
If I comment the recursive call
$subtree = array($node['children']);
$this->printTree($subtree);,
then $node['name'] isn't undefined and the code works, but of course with only with one level of depth.
SOLVED: (Thanks all guys!)
public function printTree($tree) {
$result = "";
if(is_array($tree) && count($tree) > 0) {
$result .= '<ul>';
foreach($tree as $node) {
$result .= '<li>Cat: '.$node['name'];
if (isset($node['children'])) {
$result .= $this->printTree($node['children']);
}
$result .= '</li>';
}
$result .= '</ul>';
}
return $result;
}

Answer 1

You are pushing $node['children'] into an additional array. That way you are not dealing with the subarray of this node (which has a name later on), but you have another layer of array.
Skip this array layer, remove it.
Also note that !is_null() isn't really a nice check if you then want to use that variable as an array. Check for is_array() instead, because strings and other scalar values will return count>0 as well - they return 1. Only NULL returns count=0.

Answer 2

You will have to append the results returned by the consecutive calls to printTree() for child nodes to the $result.
$result .= $this->printTree($node['children']);
:)

Answer 3

First of all, you want to enclose the $subtree-stuff into an if-condition checking for the existence of the key 'children', because as it is now, you have created an infinite loop of recursive calls to printTree(), but you only want to do this, if the key 'children' exists.
Second, I guess you want to add $result .= in front of $this->printTree($subtree);, otherwise the return value will simply be discarded.
Third, don't do $subtree = array($node['children']);. $node['children'] already is an array, so this adds another level to the array, which makes the recursion break.
So, the final function should look something like this:
public function printTree($tree) {
$result = '';
if(!is_null($tree) && count($tree) > 0) {
$result .= '<ul>';
foreach($tree as $node) {
$result .= '<li>Cat: '.$node['name'];
if (isset($node['children'])) {
$subtree = $node['children'];
$result .= $this->printTree($subtree);
}
$result .= '</li>';
}
$result .= '</ul>';
}
return $result;
}
Edit: Whoops, was too slow there, the others also found the three problems here :)