PHP Array_intersect输入未定义的偏移量

Question

I got an array working like this:

$listaMaterias[x]['id_materia'] = (value with number and letters random)
$listaMaterias[x]['name_materia'] = (string)
$listaEditoriales[x]['id_editorial'] = (value with n. and l. random)
$listaEditoriales[x]['name_editorial'] = (string)

A 'materia' is a book's category. I made a foreach where I get all values from an xml right. Many editorials and materias, where some of them comes repeated.

And then, I make a method with an array_intersect to make remove repeated values, but I get an error :

    $listaEdits_result = array();  // final results
    $listaMats_result = array();

    $listaEds_first_res = $listaEditoriales[0];
    for ($j = 1 ; $j < count($listaEditoriales) ; $j++ ){
        $listaEdits_result = array_intersect($listaEds_first_res, $listaEditoriales[$j]);
        $listaEds_first_res = $listaEdits_result;
    }

    $listaMts_first_res = $listaMaterias[0];
    for ($k = 1 ; $k < count($listaMaterias) ; $k++ ){

             // Line 285, is this one above

        $listaMats_result = array_intersect($listaMts_first_res, $listaMaterias[$j]);
        $listaMts_first_res = $listaMats_result;
    }

And finally, I get this error :

Notice: Undefined offset: 20 in [URL]/menu-librosnormales.php on line 285

Warning: array_intersect(): Argument #2 is not an array in [URL]/menu-librosnormales.php on line 285

Why access offset 20 if before I count this quantity in every array :

count($listaEditoriales) : 20

count($listaMaterias) : 14

Answer 1

Instead of $listaMaterias[$j] do $listaMaterias[$k] in second loop below line:-

$listaMats_result = array_intersect($listaMts_first_res, $listaMaterias[$j]);

Note:- If your aim is to remove duplicates from an array then you can use array_unique() easily.