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

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?

}

Baba · Accepted Answer · 2012-10-30 19:26:17Z

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

3

4

5

edited Oct 30, 2012 at 19:26

answered Oct 30, 2012 at 19:08

Baba

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9 Comments

HenchHacker Over a year ago

Not bad, except the explode("->", $ref) inside the foreach - i'm not 100% if it's the same in foreach as it is in for loops (but i would imagine it is), but shouldn't the explode be outside the foreach to prevent the explode() function getting called on every iteration... ><

Ultimater Over a year ago

This works but it doesn't check if the variable exists first, so if the reference is invalid, then it generates a warning when the echo should be skipped if it doesn't exist. Try adding: $refAr[]='b->doesnt->exist';

user1726343 Over a year ago

Just add a condition that checks if array_key_exists($v,$t) and break the loop, not output if true.

Baba Over a year ago

@VBAssassin it create a copy of the array as soon as you call foreach it does not matter if its inside or in a variable it would still create a copy .. and that is the only copy

Ultimater Over a year ago

Seems to be working, the is_array($t) part is what I was struggling with. Could you get this thing to work with array references too for references to arrays such as b->ba rather than just strings and numbers?

|

Ultimater · Accepted Answer · 2013-10-17 09:49:53Z

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>';
    }
}

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