sort stories.json

stories.php

<?php

$data = json_decode(file_get_contents('c:/tmp/stories.json'), true);
$map = ['year', 'created_at', 'title', 'url', 'points', 'author', 'num_comments'];

$file_input = fopen("stories.csv", "w");
fputcsv($file_input, $map);

foreach($data as $year => $stories) {
	foreach($stories as $story) {
		for($row = [$year], $i = 1; $i < count($map); $i++) {
			$row[$map[$i]] = $i == 1 ? date('Y-m-d H:i:s', strtotime($story['created_at'])) : $story[$map[$i]];
		}

		fputcsv($file_input, $row);
	}
}

fclose($file_input);