Sort array by inner key

gistfile1.txt

<?php
$a = Array(
    1 => Array(
         'name' => 'Peter',
         'age' => 17
    ),
    0 => Array(
         'name' => 'Nina',
         'age' => 21
    ),
    2 => Array(
         'name' => 'Bill',
         'age' => 15
    ),
);
function compareByName($a, $b) {
  return strcmp($a["name"], $b["name"]);
}
usort($a, 'compareByName');
/* The next line is used for debugging, comment or delete it after testing */
print_r($a);

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usort($array, function($a, $b){ return strcmp($a["name"], $b["name"]); });

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function cmp($a, $b)
{
        return strcmp($a["name"], $b["name"]);
}

usort($array, "cmp");