Rust Practice Exercises

Word Frequency Counter in Rust

Count how often each word appears with a HashMap and print the most common ones.

Beginner
2 min read
1 runnable example

What you'll learn

split_whitespace
entry().or_insert(0)
Sorting by count

Run code →

counts

"the"3

"brown"1

"dog"1

The word is the key, the count is the value

Counting words is a typical job for a hash map: the word is the key and the number of times it appears is the value.

entry(word).or_insert(0) returns the counter for the word, creating it at 0 the first time. The pairs are then sorted by count, highest first, and by word when the counts are equal, so the output is always the same.

Key points

entry creates the counter the first time.
Sort by count, then by word.
take(3) keeps the top three.

Runnable Rust example

Rust

Run code →

main.rs

use std::collections::HashMap;

fn main() {
    let text = "the quick brown fox jumps over the lazy dog the end";
    let mut counts: HashMap<&str, u32> = HashMap::new();

    for word in text.split_whitespace() {
        *counts.entry(word).or_insert(0) += 1;
    }

    let mut entries: Vec<(&str, u32)> = counts.into_iter().collect();
    entries.sort_by(|a, b| b.1.cmp(&a.1).then(a.0.cmp(b.0)));

    for (word, count) in entries.iter().take(3) {
        println!("{word}: {count}");
    }
}

Get a Run button for this example Result of running the code

the: 3
brown: 1
dog: 1

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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