<?php
/**
 * Created by PhpStorm.
 * User: npisarev
 * Date: 03/12/2016
 * Time: 11:46
 */

$data1 = [
    'parent.child.field'      => 1,
    'parent.child.field2'     => 2,
    'parent2.child.name'      => 'test',
    'parent2.child2.name'     => 'test',
    'parent2.child2.position' => 10,
    'parent3.child3.position' => 10,
];

$data  = [
    'parent'  => [
        'child' => [
            'field'  => 1,
            'field2' => 2,
        ],
    ],
    'parent2' => [
        'child'  => [
            'name' => 'test',
        ],
        'child2' => [
            'name'     => 'test',
            'position' => 10,
        ],
    ],
    'parent3' => [
        'child3' => [
            'position' => 10,
        ],
    ],
];

function constructive(array $data)
{
    $result = [];
    foreach ($data as $key => $value) {
        list($parent, $child, $arg) = explode('.', $key);
        $result[$parent][$child][$arg] = $value;
    }

    return $result;
}


function recursive(array $data, $keys = [])
{
    $result = [];
    foreach ($data as $key => $value) {
        if (is_array($value)) {
            $keys[]   = $key;
            $result = array_merge($result, recursive($value, $keys));
            array_pop($keys);
            continue;
        }
        $resKey          = implode('.', $keys);
        $result[$resKey . '.' .$key] = $value;
    }
    return $result;
}

print_r(constructive($data1));

print_r(recursive($data));