Nesting a variable number of keys to create a multidimensional array without using eval()

Question

I've created a function that returns a nested array based in the values and keys of another two arrays and assigns a third value to the deepest key (hope it makes any sense with the code):

function myfunc_build_array($mydata,$keys,$value)
{
    $newarr=array();

    foreach ($mydata as $data)
    {
        $evalvar='$newarr';     
        foreach ($keys as $key)
        {           
            $evalvar.="['".$data[$key]."']";
        }
        $evalvar.='=$value;';
        eval($evalvar); 
    }
    return $newarr;
}

So, i.e. if we have:

$mydata=array(
      0=>array('section'=>'NS1','subsection'=>'NS1A','employee'=>'2812','name'=>'Bob'),
      1=>array('section'=>'NS1','subsection'=>'NS1A','employee'=>'2811','name'=>'Bib'),
      2=>array('section'=>'NS1','subsection'=>'NS1B','employee'=>'2718','name'=>'Bub'),
    );

$keys= array('section','subsection','employee');

The result for myfunc_build_array($mydata,$keys,"active"); is:

array(1) {
  ["NS1"]=>
  array(2) {
    ["NS1A"]=>
    array(2) {
      [2812]=>
      string(6) "active"
      [2811]=>
      string(6) "active"
    }
    ["NS1B"]=>
    array(1) {
      [2718]=>
      string(6) "active"
    }
  }
}

It works fine but as I usually avoid using eval(), I was wondering if there is a better way to do it, more elegant or faster.

Lèse majesté · Accepted Answer · 2012-07-13 12:51:22Z

2

There is a way to do it without eval() by using references. Don't know if it's faster, but it's perhaps safer:

function myfunc_build_array($keySets,$keyIndices,$value)
{
    $slot = null;
    $newarr=array();
    foreach ($keySets as $keys)
    {
        $slot = &$newarr;
        foreach ($keyIndices as $keyIndex)
        {           
            $slot = &$slot[$keys[$keyIndex]];
        }
        $slot = $value;
    }
    return $newarr;
}

answered Jul 13, 2012 at 12:51

Lèse majesté

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Comments

nickb · Accepted Answer · 2012-07-13 12:44:30Z

1

This worked for me, although I wouldn't necessarily call it elegant:

function myfunc_build_array($mydata,$keys,$value)
{
    $newarr = array();

    end( $keys);
    $last_key = key( $keys);

    foreach ($mydata as $data)
    {  
        $temp =& $newarr; 
        foreach ($keys as $i => $key)
        {           
            $temp[$data[$key]] = isset( $temp[$data[$key]]) ? $temp[$data[$key]] : ($last_key === $i ? $value : array());
            $temp =& $temp[$data[$key]];
        }
    }

    return $newarr;
}

You can see that it produces this output:

array(1) {
  ["NS1"]=>
  array(2) {
    ["NS1A"]=>
    array(2) {
      [2812]=>
      string(6) "active"
      [2811]=>
      string(6) "active"
    }
    ["NS1B"]=>
    array(1) {
      [2718]=>
      string(6) "active"
    }
  }
}

answered Jul 13, 2012 at 12:44

nickb

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3 Comments

Lèse majesté Over a year ago

Are there any potential problems if you don't explicitly create each level of the array and simply set a reference to $temp['level1'] where $temp = array(); In my experience, PHP just creates the key without throwing any errors when you do this.

nickb Over a year ago

Probably not - I always try to so it's more clear what's going on.

Lèse majesté Over a year ago

Gotcha. I guess it's probably also the safer thing to do since the PHP manual doesn't really specify what the standard behavior is when you do that.

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