How array_reduce() and array_map() Behave with Associative Arrays in PHP

results.txt

On PHP 7.2.24-0ubuntu0.18.04.1 (cli) (built: Oct 28 2019 12:07:07) ( NTS ):
Array
(
    [a] => ABC: 1
    [b] => ABC: 2
)

,1,2

test.php

<?php

$x = [
  'a' => 1,
  'b' => 2,
];

$y = array_map(function ($value) { return 'ABC: ' . $value; }, $x);

print_r($y);
print "\n";

$z = array_reduce($x, function ($memo, $value) { return $memo . ',' . $value; });

print_r($z);
print "\n";
print "\n";