How to use map that has more than one output?

So far I use the map function as a 1-1 relationship, such as the following example:

let vector = [1, 2, 3];
let result: Vec<_> = vector.iter().map(|x| x * 2).map(|x| x + 1).collect();
println!("After mapping: {:?}", result);
// After mapping: [3, 5, 7]

In this example there are 2 map function and both function are having a 1-1 relationship. I would like to know how could I change the code such that the first map function could provide output multiple (e.g. 2) output to the second map function?

>Solution :

To achieve a 1-to-many relationship in the context of your example, you can use the flat_map function. Here’s how you can modify your code:

let vector = [1, 2, 3];
let result: Vec<_> = vector
    .iter()
    .flat_map(|x| vec![x * 2, x * 3]) // Modify this line to produce multiple outputs
    .map(|x| x + 1)
    .collect();
println!("After mapping: {:?}", result);

In this example, flat_map takes a closure that produces an iterator, and the results are flattened into a single iterator. Here, I used vec![x * 2, x * 3] to produce two outputs for each element in the original vector. The subsequent map then operates on each of these values, resulting in the final mapped vector [3, 4, 5, 6, 7, 10].