Function flat_map 

pub fn flat_map<T, R, F>(collection: &[T], iteratee: F) -> Vec<R>
where
    F: Fn(&T, usize) -> Vec<R>,

Apply a function to each item in a collection, flattening the results based on a callback.

This function iterates over a collection and applies the provided iteratee function to each item along with its index. The iteratee returns a vector of transformed items, which are then concatenated into a single resulting vector.

Arguments

• collection - A slice of items.
• iteratee - A function that takes a reference to an item and its index, returning a vector of transformed items.

Returns

• Vec<R> - A vector containing all the transformed items from each iteration.

Examples

use lowdash::flat_map;
let numbers = vec![1, 2, 3];
// For each number, generate a vector containing the number and its double
let result = flat_map(&numbers, |x, _| vec![*x, *x * 2]);
assert_eq!(result, vec![1, 2, 2, 4, 3, 6]);

use lowdash::flat_map;

#[derive(Debug, PartialEq)]
struct Person {
    name: String,
    hobbies: Vec<String>,
}

let people = vec![
    Person {
        name: "Alice".to_string(),
        hobbies: vec!["Reading".to_string(), "Cycling".to_string()],
    },
    Person {
        name: "Bob".to_string(),
        hobbies: vec!["Cooking".to_string()],
    },
];

// Extract all hobbies from the list of people
let all_hobbies: Vec<String> = flat_map(&people, |person, _| person.hobbies.clone());
assert_eq!(
    all_hobbies,
    vec![
        "Reading".to_string(),
        "Cycling".to_string(),
        "Cooking".to_string()
    ]
);