Push and pop
- Rust course
- Beginner
- Lesson 95/115
- 4 min
Add and remove elements with push and pop.
Adding and removing
Methods that change the vector need a mut variable:
let mut v = vec![1, 2];
v.push(3); // add to the end: [1, 2, 3]
v.insert(0, 0); // add at position 0: [0, 1, 2, 3]
let son = v.pop(); // Some(3): [0, 1, 2]
let ilk = v.remove(0);// 0: [1, 2]pop is safe on an empty vector too (it returns None), because the result is an Option<T>. remove and insert panic on an invalid index.
Bulk operations
To add or remove several elements at once:
let mut v = vec![1, 2];
v.extend([3, 4, 5]); // [1, 2, 3, 4, 5]
v.truncate(3); // [1, 2, 3]
let kalan: Vec<i32> = v.drain(1..).collect(); // v = [1], kalan = [2, 3]
v.clear(); // []swap_remove(i) replaces the element with the last one and removes it; the order breaks but it's O(1).
Practice Add and remove
Start with let mut v = vec![1, 2];. Apply push(3), insert(0, 0), let son = v.pop(); and let ilk = v.remove(0); in order. Print v, son ({:?}) and ilk on one line.
Starter code
fn main() {
// buraya yaz
}Sample solution
fn main() {
let mut v = vec![1, 2];
v.push(3);
v.insert(0, 0);
let son = v.pop();
let ilk = v.remove(0);
println!("{:?} {:?} {}", v, son, ilk);
}Expected output
[1, 2] Some(3) 0
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the performance difference between <code>insert(0, x)</code> and <code>push(x)</code>?
- insert doesn't allocate
- insert(0, ..) shifts every element (O(n)); push is usually O(1) Correct answer
- There is no difference
- push is slower
Explanation: If you often add to the front, VecDeque is a better fit.
2 Pull from the end
let mut v = vec![1, 2, 3];
let son = v.____(); // Some(3)let mut v = vec![1, 2, 3];
let son = v.pop(); // Some(3)Explanation: pop removes the last element and returns it inside an Option.
3 Method and effect on [1, 2, 3]
| Term | Meaning |
|---|---|
push(4) |
[1, 2, 3, 4] |
pop() |
Some(3) |
remove(0) |
Returns 1 |
insert(1, 9) |
[1, 9, 2, 3] |