itertools & rand

itertools extends the iterator ecosystem with combinators std lacks. rand provides reproducible, testable randomness for simulations, sampling, and IDs.

Recipe

itertools = "0.14"
rand = "0.9"

use itertools::Itertools;
 
fn main() {
    let v = vec![1, 2, 3, 4];
    let pairs: Vec<_> = v.iter().tuple_windows().collect();
    assert_eq!(pairs, vec![(&1, &2), (&2, &3), (&3, &4)]);
}

use rand::Rng;
 
fn sample_id() -> u64 {
    rand::rng().random_range(1_000_000..9_999_999)
}

When to reach for this:

• Chunking, grouping, and cartesian products in ETL
• Shuffling test fixtures
• Game logic, Monte Carlo, load test data

Working Example

use itertools::iproduct;
use rand::seq::SliceRandom;
 
fn all_pairs(ids: &[u32]) -> Vec<(u32, u32)> {
    iproduct!(ids.iter(), ids.iter())
        .map(|(&a, &b)| (a, b))
        .filter(|(a, b)| a < b)
        .collect()
}
 
fn shuffled(mut items: Vec<&str>) -> Vec<&str> {
    items.shuffle(&mut rand::rng());
    items
}

What this demonstrates:

• iproduct! replaces nested loops
• tuple_windows for sliding views
• SliceRandom for unbiased shuffles

Deep Dive

itertools Highlights

Reproducible RNG

use rand::SeedableRng;
use rand::rngs::StdRng;
 
let mut rng = StdRng::seed_from_u64(42);
let n: u32 = rng.random_range(0..100);

Seed in tests for deterministic output.

Gotchas

• rand in security contexts - thread_rng is not crypto. Fix: rand_core + ring or OS RNG for tokens.
• Collecting infinite iterators - hangs. Fix: take(n) before collect.
• itertools in public APIs - couples consumers to crate. Fix: return Vec or impl Iterator where possible.
• Bias in random_range - use library ranges, not % on integers.
• Large cartesian products - memory explosion. Fix: stream with for_each instead of collect.

Alternatives

FAQs

Related

• Iterator adapters
• rayon - parallel collect
• Collections basics
• Essential Crates Best Practices

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.