$newData = array (
    array(
        'id' => 1,
        'name' => 'John',
        'sex' => 'male'
    ),
    array(
        'id' => 2,
        'name' => 'Kenny',
        'sex' => 'male',
    ),
    array(
        'id' => 3,
        'name' => 'Sarah',
        'sex' => 'female'
    ),
    array(
        'id' => 4,
        'name' => George,
        'sex' => male,
    )
);

$oldData = array(
    array(
        'id' => 3,
        'name' => 'Sarah',
        'sex' => 'female'
    ),
    array(
        'id' => 4,
        'name' => 'George',
        'sex' => 'male'
    ),
    array(
        'id' => 5,
        'name' => 'Peter',
        'sex' => 'male'
    ),
    array(
        'id' => 6,
        'name' => 'Lexi',
        'sex' => 'female'
    )
);



$tmpArray = array();

foreach($newData as $data1) {

  $duplicate = false;
  foreach($oldData as $data2) {
    if($data1['id'] === $data2['id'] && $data1['name'] === $data2['name'] && $data1['sex'] === $data2['sex']) $duplicate = true;
  }

  if($duplicate === false) $tmpArray[] = $data1;
}

$newData = $tmpArray;

echo '<pre>';
print_r($newData);
echo '</pre>';