Summary - Vectors

Combine push, get and for to build a shopping cart.

Vectors summary

Vec<T> is a growable array living on the heap. Creating: Vec::new(), vec![..], vec![x; n], with_capacity. Changing: push, pop (Option), insert, remove, extend, clear. Reading: v[i] (panic risk) or get (Option). Looping: &v reads, &mut v modifies, v consumes.

Sorting and filtering

Useful methods that work in place:

let mut v = vec![5, 3, 8, 3, 1, 8];
v.sort();                  // [1, 3, 3, 5, 8, 8]
v.dedup();                 // [1, 3, 5, 8]
v.retain(|&x| x > 2);      // [3, 5, 8]
v.reverse();               // [8, 5, 3]

Floating-point numbers can't be sorted with sort (because of NaN); v.sort_by(|a, b| a.total_cmp(b)) is used.

Exercise Clean and filter

For let mut v = vec![5, 3, 8, 3, 1, 8];, apply sort, dedup and retain(|&x| x > 2) in order; print the result with {:?}.

Show example solution

fn main() {
    let mut v = vec![5, 3, 8, 3, 1, 8];
    v.sort();
    v.dedup();
    v.retain(|&x| x > 2);
    println!("{:?}", v);
}

Test yourself

What is <code>v</code> after <code>let mut v = vec![3, 1, 3, 2]; v.sort(); v.dedup();</code>?
- [1, 3, 2]
- [1, 2, 3]
- [1, 2, 3, 3]
- [3, 1, 2]
Show answer

[1, 2, 3] — dedup only removes consecutive duplicates, which is why sort is needed first.

Keep by condition

let mut v = vec![1, 3, 5, 8];
v.____(|&x| x > 2);   // [3, 5, 8]

Show answer

let mut v = vec![1, 3, 5, 8];
v.retain(|&x| x > 2);   // [3, 5, 8]

Method and effect

sort()

Ascending
dedup()

Removes consecutive duplicates
retain(..)

Keeps matching ones
reverse()

Reverses the order

Next lesson: String and &str conversion

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