- print_r: documentation ( source)
- array_keys: documentation ( source)
- uksort: documentation ( source)
<?php
$edge_lengths = [420, 593.9696961967, 420];
uksort($edge_lengths, fn($k1, $k2) => $edge_lengths[$k2] <=> $edge_lengths[$k1] ?: $k2 <=> $k1);
print_r(array_keys($edge_lengths));