Rust: What is the difference between retain and remove?

retain — keep matching. remove — remove by index.

retain:

• Keep matching items.
• Predicate-based.
• Bulk operation.

remove:

• Remove by index.
• Returns element.
• Single operation.

1let mut v = vec![1, 2, 3, 4, 5];
2v.retain(|&x| x % 2 == 0);
3// v: [2, 4]
4
5let mut v = vec![1, 2, 3, 4, 5];
6let removed = v.remove(2);
7// removed: 3, v: [1, 2, 4, 5]

Key: retain for filtering, remove for index-based.