<?php 

$liste=array("a","b","c","d","e");



//La position de l'element à extraire( ici ce sera "c")

$position_element=2;



array_splice ($liste, $position_element,1);



//Affiche Array ( [0] => a [1] => b [2] => d [3] => e )

print_r($liste); 

<?php 

$liste=array("a","b","c","e");



//La position de l'element à ajouter( ici ce sera "d")

$position_element=3;



array_splice ($liste, $position_element,0,array("d"));



//Affiche Array ( [0] => a [1] => b [2] => c [3] => d [4] => e )

print_r($liste);