Count How Often Each Item Appears

Fold a slice into a HashMap that maps each value to how many times it occurs, incrementing the entry on each pass.

Language: Rust

Added on: 21^st August 2026

Submitted by: Lupraxus

use std::collections::HashMap;
use std::hash::Hash;

fn frequency_count<T: Copy + Eq + Hash>(items: &[T]) -> HashMap<T, usize> {
    items.iter().fold(HashMap::new(), |mut acc, &item| {
        *acc.entry(item).or_insert(0) += 1;
        acc
    })
}

Caveats

Needs T: Copy + Eq + Hash. Use Clone instead of Copy if the items are not Copy.