n-dimensional arrays

<?php
    /**
     * Functions for examining and manipulating matrices (n-dimensional arrays) of data
     * with string dot-separated paths. For example, you might do this with multidimensional
     * array:
     *   $var = $array['someKey']['cats']['dogs']['potato'];
     *
     * Accomplishing this can be a nightmare if you don't know the depth of the path or the array
     * is of a variable dimension.
     *
     * You can accomplish the same by using $array as a Matrix:
     *   $array = new Matrix($array);
     *   $var = $array->get('someKey.cats.dogs.potato);
     *  
     * @author Daniel Tomasiewicz <www.fourstaples.com>
     */
    class Matrix {
        private $data;
       
        public function __construct(array $data = array()) {
            $this->data = $data;
        }
       
        /**
         * Gets the value at the specified path.
         */
        public function get($path = null) {
            if($path === null) {
                return $this->data;
            }
           
            $segs = explode('.', $path);
           
            $target =& $this->data;
            for($i = 0; $i < count($segs)-1; $i++) {
                if(isset($target[$segs[$i]]) && is_array($target[$segs[$i]])) {
                    $target =& $target[$segs[$i]];
                } else {
                    return null;
                }
            }
           
            if(isset($target[$segs[count($segs)-1]])) {
                return $target[$segs[count($segs)-1]];
            } else {
                return null;
            }
        }
       
        /**
         * Sets a value to a specified path. If the provided value is
         * null, the existing value at the path will be unset.
         */
        public function set($path, $value = null) {
            if(is_array($path)) {
                foreach($path as $p => $v) {
                    $this->set($p, $v);
                }
            } else {
                $segs = explode('.', $path);
           
                $target =& $this->data;
                for($i = 0; $i < count($segs)-1; $i++) {
                    if(!isset($target[$segs[$i]])) {
                        $target[$segs[$i]] = array();
                    }
                   
                    $target =& $target[$segs[$i]];
                }
           
                if($segs[count($segs)-1] == '*') {
                    foreach($target as $key => $value) {
                        $target[$key];
                    }
                } elseif($value === null && isset($target[$segs[count($segs)-1]])) {
                    unset($target[$segs[count($segs)-1]]);
                } else {
                    $target[$segs[count($segs)-1]] = $value;
                }
            }
        }
       
        /**
         * Returns a flattened version of the data (one-dimensional array
         * with dot-separated paths as its keys).
         */
        public function flatten($path = null) {
            $data = $this->get($path);
           
            if($path === null) {
                $path = '';
            } else {
                $path .= '.';
            }
           
            $flat = array();
                       
            foreach($data as $key => $value) {
                if(is_array($value)) {
                    $flat += $this->flatten($path.$key);
                } else {
                    $flat[$path.$key] = $value;
                }
            }
           
            return $flat;
        }
       
        /**
         * Expands a flattened array to an n-dimensional matrix.
         */
        public static function expand($flat) {
            $matrix = new Matrix();
           
            foreach($flat as $key => $value) {
                $matrix->set($key, $value);
            }
           
            return $matrix;
        }
    }
?>