Referencing a multidimensional array's elements based on a string without eval - php

Question

Alright I'm working with a large multidimensional array which has more information in it than I need and I want to loop through it to filter the data which I'm interested in. Sadly this multidimensional array is produced dynamically and doesn't always contain the data I want, so I have to use logic like:
if(isset($ar['b']['ba']['baa'])){
echo '<h3>'.$ar['b']['ba']['baa'].'</h3>';
}
if(isset($ar['b']['ba']['baba'])){
echo '<h3>'.$ar['b']['ba']['baba'].'</h3>';
}
if(isset($ar['b']['ba']['babb'])){
echo '<h3>'.$ar['b']['ba']['babb'].'</h3>';
}
The above works great but its a bit messy-looking so I converted the above to:
$refAr=array();
$refAr[]='b->ba->baa';//3
$refAr[]='b->ba->bab->baba';//4
$refAr[]='b->ba->bab->babb';//5
The above looks a lot more nice and neat and is how I want to control the script in case I need to reference different keys in the future. The problem I am having is trying to use the above format to actually reference the array. I thought variable variables would work but apparently it fails. My second attempt using eval worked but I'm not very happy with my solution. This is where I need you guys to come in, is there a better way to do this? Here's my attempt below:
<?php
$ar=array(
'a'=>array('aa'=>1,'ab'=>2),
'b'=>array(
'ba'=>array('baa'=>3,'bab'=>array('baba'=>4,'babb'=>5),'bac'=>array('baca'=>6,'bacb'=>7)),
)
);
$refAr=array();
$refAr[]='b->ba->baa';//3
$refAr[]='b->ba->bab->baba';//4
$refAr[]='b->ba->bab->babb';//5
foreach($refAr as $ref)
{
$r=explode('->',$ref);
$r="\$ar['".implode("']['",$r)."']";
echo '<h1>'.$r.'</h1>';
echo '<h3>'.$$r.'</h3>';//undefined
eval('$t='.$r.';');
echo "<h3>$t</h3>";//works but uses eval, is there a better way?
}

Answer 1

You can try
$ar = array();
$ar['b']['ba']['baa'] = 3;
$ar['b']['ba']['bab']['baba'] = 4;
$ar['b']['ba']['bab']['babb'] = 5;
$refAr = array();
$refAr[] = 'b->ba->baa'; // 3
$refAr[] = 'b->ba->bab->baba'; // 4
$refAr[] = 'b->ba->bab->babb'; // 5
foreach ( $refAr as $ref ) {
$t = $ar;
foreach ( explode("->", $ref) as $v ) {
if (!isset($t[$v]))
break;
$t = $t[$v];
}
is_array($t) and $t = null;
echo "<h3>$t</h3>";
}
Output
345

Answer 2

I decided to answer my own question. This is what I wound up using:
<?php
//Sample PHP representation of dynamically-pulled JSON data from an untrusted source
$ar=array(
'a'=>array('aa'=>1,'ab'=>2),
'b'=>array(
'ba'=>array('baa'=>3,'bab'=>array('baba'=>4,'babb'=>5),'bac'=>array('baca'=>6,'bacb'=>7)),
)
);
//Reusable function
function resolveReference($ar,&$ref)
{
$t = $ar;
foreach ( explode('->',$ref) as $v )
{
if (!array_key_exists($v,$t)){$ref=null;return false;}
$t = $t[$v];
}
$ref=$t;
return true;
}
//The references I'm interested in but don't know if my dynamic data will contain these keys every time
$refAr=array();
$refAr[]='b->ba->baa';
$refAr[]='b->ba->bab->baba';
$refAr[]='b->ba->bab->babb';
$refAr[]='b->doesnt->exist';
foreach($refAr as $ref)
{
echo '<h1>'.$ref.'</h1>';
if(resolveReference($ar,$ref))
{
echo '<h3><span style="color:blue;">'.$ref.'</span></h3>';
}else{
echo '<h3><span style="color:red;">Alternative text for non-existent expected reference</span></h3>';
}
}