Question

I am trying to read data (which is actually an array) in Lisp from a text file.
I tried to use with-open-file and read-line stuff but could not achieve my goal. What I am looking for is equivalent to doing data=load('filename.txt') in MATLAB, so that I get an array called data which has loaded the whole information in filename.txt.

The text file will be in a format like

1.0 2.0 3.0 ...
1.5 2.5 3.5 ...
2.0 3.0 4.0 ...
 .....

The size may also vary. Thanks a lot in advance.

Answer 1

The basic way to do that is to use with-open-file for getting the input stream, read-line in a loop to get the lines, split-sequence (from the library of the same name) to split it into fields, and parse-number (from the library of the same name) to transform the strings into numbers. All libraries mentioned are available from Quicklisp.

EDIT: Just to get you started, this is a simple version without validation:

(defun load-array-from-file (filename)
  (with-open-file (in filename
                      :direction :input)
    (let* ((data-lol (loop :for line := (read-line in nil)
                           :while line
                           :collect (mapcar #'parse-number:parse-number
                                            (cl-ppcre:split "\\s+" line))))
           (rows (length data-lol))
           (columns (length (first data-lol))))
      (make-array (list rows columns)
                  :initial-contents data-lol))))

You should add some checks and think about what you want to get in case they are not fulfilled:

• Are the rows all the same length?
• Are all fields valid numbers?