Laravel Collections: flip() for Instant Lookups

Here’s a Laravel Collection performance trick: use flip() to turn expensive searches into instant lookups.

I was looping through a date range, checking if each date existed in a collection. Using contains() works, but it’s O(n) for each check — if you have 100 dates to check against 50 items, that’s 5,000 comparisons.

// Slow: O(n) per check
$available = collect(['2026-01-25', '2026-01-26', '2026-01-27']);
if ($available->contains($date)) { ... }

The fix — flip() converts values to keys, making lookups O(1):

// Fast: O(1) per check
$available = collect(['2026-01-25', '2026-01-26'])
    ->flip(); // Now: ['2026-01-25' => 0, '2026-01-26' => 1]

if ($available->has($date)) { ... }

For small datasets, the difference is negligible. But checking hundreds or thousands of items? This tiny change saves significant processing time. Costs nothing to implement.