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to Nucleotide Count in the Common Lisp Track

Published at Mar 09 2020 · 0 comments
Test suite

Given a single stranded DNA string, compute how many times each nucleotide occurs in the string.

The genetic language of every living thing on the planet is DNA. DNA is a large molecule that is built from an extremely long sequence of individual elements called nucleotides. 4 types exist in DNA and these differ only slightly and can be represented as the following symbols: 'A' for adenine, 'C' for cytosine, 'G' for guanine, and 'T' thymine.

Here is an analogy:

  • twigs are to birds nests as
  • nucleotides are to DNA as
  • legos are to lego houses as
  • words are to sentences as...


Check out Installing Common Lisp for instructions to get started or take a look at the guides available in the track's side bar.


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One suggested add-on for Emacs and Common Lisp is SLIME which offers tight integration with the REPL; making iterative coding and testing very easy.


The Calculating DNA Nucleotides_problem at Rosalind http://rosalind.info/problems/dna/

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


(ql:quickload "lisp-unit")
#-xlisp-test (load "nucleotide-count")

(defpackage #:nucleotide-count-test
  (:use #:common-lisp #:lisp-unit))

(in-package #:nucleotide-count-test)

(defun make-hash (kvs)
   #'(lambda (h kv) (setf (gethash (first kv) h) (second kv)) h)
   :initial-value (make-hash-table)))

(define-test empty-dna-strand-has-no-adenine
  (assert-equal 0 (dna:dna-count #\A "")))

(define-test empty-dna-strand-has-no-nucleotides
  (assert-equalp (make-hash '((#\A 0) (#\T 0) (#\C 0) (#\G 0)))
      (dna:nucleotide-counts "")))

(define-test repetitive-cytosine-gets-counted
  (assert-equal 5 (dna:dna-count #\C "CCCCC")))

(define-test repetitive-sequence-has-only-guanine
  (assert-equalp (make-hash '((#\A 0) (#\T 0) (#\C 0) (#\G 8)))
      (dna:nucleotide-counts "GGGGGGGG")))

(define-test counts-only-thymine
  (assert-equal 1 (dna:dna-count #\T "GGGGGTAACCCGG")))

(define-test validates-nucleotides
  (assert-error 'dna:invalid-nucleotide (dna:dna-count #\X "GACT")))

(define-test counts-all-nucleotides
  (assert-equalp (make-hash '((#\A 20) (#\T 21) (#\G 17) (#\C 12)))

(let ((*print-errors* t)
      (*print-failures* t))
  (run-tests :all :nucleotide-count-test))
(in-package #:cl-user)
(defpackage #:dna
  (:use #:common-lisp)
  (:export #:dna-count #:nucleotide-counts #:invalid-nucleotide))

(in-package #:dna)

(defvar nucleotides '(#\A #\G #\C #\T))

(define-condition invalid-nucleotide (error) ())

(defun dna-count (nucleotide dna)
  (if (member nucleotide nucleotides)
        ((matches-nucleotide (character)
          (char= nucleotide character)))
        (count-if #'matches-nucleotide (coerce dna 'list)))
      (error 'invalid-nucleotide)))

(defun nucleotide-counts (dna)
    ((dna-count-add (table nucleotide)
      (setf (gethash nucleotide table)
            (dna-count nucleotide dna))
    (reduce #'dna-count-add
            :initial-value (make-hash-table))))

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