How to filter a Vec

Use the filter method on the vector's iterator with a closure that returns true for items you want to keep, then call collect() to create a new vector.

let filtered: Vec<Shoe> = shoes
    .into_iter()
    .filter(|s| s.size == 10)
    .collect();

This pattern works for any condition, such as checking if a string contains a substring:

let results: Vec<&str> = contents
    .lines()
    .filter(|line| line.contains(query))
    .collect();

Filtering a vector is like sorting a pile of mail to keep only the letters addressed to you. You go through each item one by one, check a specific rule, and put the matching items into a new pile. This lets you quickly extract exactly the data you need from a larger list without writing manual loops.