map and filter

Transform iterators with the map and filter adaptors.

map and filter

map and filter are adapters returning a new iterator. They are chained to build data-processing pipelines:

let sonuc: Vec<i32> = (1..=10)
    .filter(|n| n % 3 == 0)   // 3, 6, 9
    .map(|n| n * n)           // 9, 36, 81
    .collect();

map transforms each element, filter drops those failing the condition. filter_map does both: if the closure returns Some(x) it keeps it, if None it drops it.

Other adapters

Other commonly used adapters:

(1..=5).take(2)              // 1, 2
(1..=5).skip(3)              // 4, 5
(1..=5).rev()                // 5, 4, 3, 2, 1
(1..=5).step_by(2)           // 1, 3, 5
(1..=3).chain(7..=8)         // 1, 2, 3, 7, 8
(1..=10).take_while(|n| n * n < 20)   // 1, 2, 3, 4

Adapters only return iterators; to get a result, the chain must end with a consuming method (collect, sum, for).

Exercise Squares of multiples of three

In the range 1..=10, select the multiples of 3 with filter, square them with map, collect into a vector and print it.

Show example solution

fn main() {
    let sonuc: Vec<i32> = (1..=10).filter(|n| n % 3 == 0).map(|n| n * n).collect();
    println!("{:?}", sonuc);
}

Test yourself

What is <code>["1", "a", "3"].iter().filter_map(|s| s.parse::<i32>().ok()).sum::<i32>()</code>?
- 0
- 4
- Panic
- 13
Show answer

4 — "a" can't be parsed, becomes None and is dropped; 1 + 3 = 4.

Transform

let kareler: Vec<i32> = (1..=3).____(|n| n * n).collect();

Show answer

let kareler: Vec<i32> = (1..=3).map(|n| n * n).collect();

Chain and result

(1..=5).take(2)

1, 2
(1..=5).skip(3)

4, 5
(1..=5).step_by(2)

1, 3, 5
(1..=3).chain(7..=8)

1, 2, 3, 7, 8

Next lesson: collect

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