defining position in an array with string

Let me throw my own answer in the mix: :)

$path = "group1.group2.group3.element";
$results = array();

$parts = explode('.', $path);
$where = &$results;
foreach ($parts as $part)
{
    $where =& $where[$part];
}
$where = $value;

I don't think this will be the best one, but I tried to find out the solution as an exercise to myself :)

    $path = "group1.group2.group3.element"; //path
    $value = 2; //value

    $results = array(); //an array

    $t = explode(".",$path);    //explode the path into an array
    $n=count($t);   //number of items

    $i=0;   //a counter variable

    $r = &$results; //create the reference to the array

    foreach($t as $p)   //loop through each item
    {
        if($i == $n-1)      //if it reached the last element, then insert the value
        {
            $r[$p] = $value;
            break;
        }
        else    //otherwise create the sub arrays
        {
            $r[$p] = array();
            $r = &$r[$p];   

            $i++;
        }       
    }

    print_r($results);  //output the structure of array to verify it

    echo "<br>Value is: " . $results['group1']['group2']['group3']['element'];  //output the value to check

Hope it will work at your side too.. :)

As I commented on your own answer, you are on the right track. Very close in fact. I prefer to use recursion though, but that's only a preference, this could all be done in a linear loop just as well.

To find a node (read) this works:

function &findnode(array $path, &$collection) {
    $node = array_shift($path);

    if (array_key_exists($node, $collection)) {        
        if (count($path) === 0) {
            // When we are at the end of the path, we return the node
            return $collection[$node];
        } else {
            // Otherwise, we descend a level further
            return findnode($path, $collection[$node]);
        }
    }

    throw new RuntimeException('path not found');
}

$collection = array(
    'foo' => array(
        'bar' => array(
            'baz' => 'leafnode @ foo.bar.baz'
            )
        )
    );

$path = 'foo.bar.baz';
$node =& findnode(explode('.', $path), $collection);

var_dump($node); // Output: 'leafnode @ foo.bar.baz'

To inject a node (write) we need to modify the logic slightly to create the path as we go.

function &findnode(array $path, &$collection, $create = false) {
    $node = array_shift($path);

    // If create is set and the node is missing, we create it
    if ($create === true && ! array_key_exists($node, $collection)) {
        $collection[$node] = array();
    } 

    if (array_key_exists($node, $collection)) {        
        if (count($path) === 0) {
            // When we are at the end of the path, we return the node
            return $collection[$node];
        } else {
            // Otherwise, we descend a level further
            return findnode($path, $collection[$node], $create);
        }
    }

    throw new RuntimeException('path not found');
}

$collection = array(
    'foo' => array(
        'bar' => array(
            'baz' => 'leafnode @ foo.bar.baz'
            )
        )
    );

$path = explode('.', 'baz.bar.foo');
$leaf = array_pop($path); // Store the leaf node

// Write
$node =& findnode($path, $collection, true);
$node[$leaf] = 'foo.bar.baz injected';

var_dump($collection); // Will have the new branch 'baz.bar.foo' with the injected value at the leaf

To make all this nice and pretty, you would wrap the read and write operations in their own functions. More likely all of this inside its own class.

So using the above version of findnode, we can have these two functions to read and write from/to your collection array.

function read($path, $collection) {
    $path = explode('.', $path);
    $val =& findnode($path, $collection);

    return $val;
} 

function write($value, $path, $collection) {
    $path = explode('.', $path);
    $leaf = array_pop($path);
    $node =& findnode($path, $collection, true);

    $node[$leaf] = $value;
}

NB! This is not a complete solution or the most elegant. But you can probably figure out the rest for yourself.

I hope below code will work,

$path = "group1.group2.group3.element";
$tempArr = explode('.', $path);
$results = array();
$arrStr = '$results';
$value = 'testing';
foreach( $tempArr as $ky=>$val) {
    $arrStr .= "['".$val."']";
    ( $ky == count($tempArr) - 1 ) ? $arrStr .= ' = $value;' : '';
}
eval($arrStr);
print_r($results);