How to display all elements starting with a certain letter?

Question

1C-Bitrix

There is such a pointer. Below it is a list of all factories. It is necessary to make such functionality that when clicking on a letter, all factories whose names begin with this letter are displayed from the list.

Answer 1

1) first select all the elements to find out which letters make links and which do not.
2) When clicking on a letter, select elements by the filter "%NAME" => 'letter'

Answer 2

<?php
$arr = array("mike", "kate", "john", "michele", "paul", "samanta", "stella");

$res = array_filter($arr, function($d) {
    return mb_substr($d, 0, 1) == 'j';
});

var_dump($res);

will display
array(1) { [2]=> string(4) "john" }