Rust - map Examples - Dot Net Perls

Map. In programming languages, the term "map" means 2 things. A map function can apply a transformation to each element in an array.

Collections. The other use of "map" refers to a dictionary collection. In Rust, we have both kinds of map, but the dictionary is called a HashMap.

collect

Map function. In this example we use the iter() function to get an iterator from an array. We then invoke the map() function to uppercase all strings.

Part 1 We call iter() to get an iterator from the animals array. We pass a lambda to map(), and make each string uppercase.

iter

Part 2 We use a for-loop over the result of map() to loop over the strings, and print them to the console. All strings are now uppercase.

for

fn main() { let animals = ["bird", "frog", "cat"]; // Part 1: use iter() map to uppercase all strings. let result = animals.iter().map(|value| value.to_uppercase()); // Part 2: loop over strings and print them. for animal in result { println!("MAP: {}", animal); } }

MAP: BIRD MAP: FROG MAP: CAT

Map collection. A "map" is a dictionary as well. Here we create a HashMap, and use that as our map. The HashMap stores optional values, and we can unwrap them.

HashMap

Tip Try using the match() construct in Rust to unwrap values returned by get() on a HashMap.

match

use std::collections::HashMap; fn main() { // Create HashMap to map keys to values. let mut codes = HashMap::new(); codes.insert("abc", 1); codes.insert("def", 2); // Access value with get function. println!("{:?}", codes.get("abc")); }

Some(1)

A summary. How can we use various types of map() functionality in Rust? The answer is clear. We can use iter() and map() to translate elements, and a HashMap for an associative array.

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This page was last updated on Feb 8, 2023 (edit link).

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