Arrays & Array Methods (map, filter, reduce)

const numbers = [1, 2, 3, 4, 5];
const pairs = numbers.flatMap((n, i) => 
  numbers.slice(i + 1).map(m => [n, m])
);

All possible pairs
This generates all unique pairs of numbers: 1) flatMap combines map and flat operations, 2) Outer loop takes each number in sequence, 3) Inner map creates pairs with remaining numbers, 4) slice(i + 1) prevents duplicate pairs and self-pairs, 5) Results in [[1,2], [1,3], [1,4], [1,5], [2,3], [2,4], [2,5], [3,4], [3,5], [4,5]], 6) Common pattern for combination generation, 7) More efficient than nested loops with filtering, 8) Useful for creating relationship mappings.
Duplicate pairs
Sequential pairs
Random pairs