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Fast FASTX parsing and k-mer methods in Rust
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Needletail is a MIT-licensed, minimal-copying FASTA/FASTQ parser and k-mer processing library for Rust.

The goal is to write a fast and well-tested set of functions that more specialized bioinformatics programs can use. Needletail's goal is to be as fast as the readfq C library at parsing FASTX files and much (i.e. 25 times) faster than equivalent Python implementations at k-mer counting.


extern crate needletail;
use needletail::{parse_sequence_path, Sequence};
use std::env;

fn main() {
    let filename: String = env::args().nth(1).unwrap();

    let mut n_bases = 0;
    let mut n_valid_kmers = 0;
        |_| {},
        |seq| {
            // is the name of the record
            // seq.seq is the base sequence
            // seq.qual is an optional quality score

            // keep track of the total number of bases
            n_bases += seq.seq.len();

            // normalize to make sure all the bases are consistantly capitalized
            let norm_seq = seq.normalize(false);
            // we make a reverse complemented copy of the sequence first for
            // `canonical_kmers` to draw the complemented sequences from.
            let rc = norm_seq.reverse_complement();
            // now we keep track of the number of AAAAs (or TTTTs via
            // canonicalization) in the file; note we also get the postion (i.0;
            // in the event there were `N`-containing kmers that were skipped)
            // and whether the sequence was complemented (i.2) in addition to
            // the canonical kmer (i.1)
            for (_, kmer, _) in norm_seq.canonical_kmers(4, &rc) {
                if kmer == b"AAAA" {
                    n_valid_kmers += 1;
    .expect("parsing failed");
    println!("There are {} bases in your file.", n_bases);
    println!("There are {} AAAAs in your file.", n_valid_kmers);


Needletail requires rust and cargo to be installed. Please use either your local package manager (homebrew, apt-get, pacman, etc) or install these via rustup.

Once you have Rust set up, you can include needletail in your Cargo.toml file like:

needletail = "^0.3.1"

To install needletail itself for development:

git clone
cargo test  # to run tests

Getting Help

Questions are best directed as GitHub issues. We plan to add more documentation soon, but in the meantime "doc" comments are included in the source.


Please do! We're happy to discuss possible additions and/or accept pull requests.

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