During implementation and testing of different small hobby projects I often reach the point where I need (at least I like it more) some random data beyond the usual foo-bar strings or lists. Random here does not mean really mathematical random data but just something that looks random to humans.

Therefore I came up with the following:

;;;; random.lisp
;;; Time-stamp: <2019-05-27 14:53:38 m.buchmann>
;;; A short sketch of some random data generating functions.

(ql:quickload "alexandria")

;; * Choosing a random element from a given list. 
(defun random-draw (list &aux (len (length list)) (pos (random len)))
  "Returns a random element from LIST."
  (nth pos list))

;;; * Generating a random element
(defun random-element (type &key (radix 10) (case :up))
  "Returns a random element of type :digit (depending on :radix) or
  :character (case given by :case :up, :down or :both). Limited to
7bit ASCII characters from A to z."
  (let ((char-range (ecase case
                      (:up   (alexandria:iota 26 :start 65))
                      (:down (alexandria:iota 26 :start 97))
                      (:both (append (alexandria:iota 26 :start 65)
                                     (alexandria:iota 26 :start 97))))))
      (ecase type
        (:digit (random radix))
        (:character (code-char (random-draw char-range))))))

(defun random-list (len &key (type :digit) (radix 10) (case :up))
  "Returns a list of length LEN filled with random elements of TYPE :digit or :character."
  (loop :for i from 0 below len
        :collect (random-element type :radix radix :case case)))

(defun random-string (len &key (case :up) &aux (result (make-array len :element-type 'character)))
  "Returns a random string of length LEN and :case (:up, :down or :both)."
  (loop :for i :from 0 :below len
        :do (setf (aref result i) (random-element :character :case case)))

I did not pack it in a proper package etc. yet because my use case is pretty simple and usually temporary. I was wondering if other people have implemented similar things or if the need I felt was just so individual that no one else really cares about it. I did not find other libraries for this.

I think it could be easily extended to supply random-arrays, hash-tables and so on. Also the character encoding could be improved to deliver more than 7bit ASCII and this in a portable way.

Any comments on the usability, style etc. are gratefully acknowledged.


2 Answers 2


Note that Alexandria defines random-elt (and whichever).

My only complain is that random-element does too much, both digits and characters. This would be the kind of use cases where I would rely on generic functions:

(defgeneric generate (type &key &allow-other-keys))

(defmethod generate ((type (eql :number/offset)) &key offset length)
  (+ offset (random length)))

(defmethod generate ((type (eql :number/around)) &key (origin 0) (length 1.0))
  (generate :number/offset
            :offset (- origin (/ length 2))
            :length length))

(defmethod generate ((type (eql :ascii)) &key case)
  (multiple-value-bind (offset length)
      (ecase case
        (:down (values 97 26))
        (:up (values 65 26))
        (:both (values 65 52)))
     (generate :number/offset :offset offset :length length))))

(defmethod generate ((type (eql :digit)) &key radix)
  (random radix))

(defmethod generate ((type (eql :choose-from)) &key sequence)
  (random-elt sequence))

For example:

(list (generate :ascii :case :up)
      (generate :digit :radix 8)
      (generate :number/around :origin 0 :length 10)
      (generate :choose-from :sequence #(5 6 8)))
  • 1
    \$\begingroup\$ Using generic functions is the right way here, of course. Thanks for reminding me ;-) \$\endgroup\$ May 28, 2019 at 11:56

Within python there is the faker package creating "human" data. It's often used for testing and can easily be extended to your personal needs:

Link to github

It also has a command line interface. Here is the example from the official documentation:

$ faker address
968 Bahringer Garden Apt. 722
Kristinaland, NJ 09890

$ faker -l de_DE address
Samira-Niemeier-Allee 56
94812 Biedenkopf

$ faker profile ssn,birthdate
{'ssn': u'628-10-1085', 'birthdate': '2008-03-29'}

$ faker -r=3 -s=";" name
Willam Kertzmann;
Josiah Maggio;
Gayla Schmitt;

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