Parse Tab Delimited String

1

votes

I'm having some trouble figuring out how to separate a string which is tab delimited into chunks of data as an example if i have a text file which I'm reading from that looks like this

a1     b1     c1     d1     e1
a2     b2     c2     d2     e2

and i read the first line of my file and get a string which of

"a1     b1     c1     d1      e2"

I want to separate this into 5 variables a,b,c,d and e, or create a list (a b c d e). Any thoughts?

Thanks.

parsinglispcommon-lisptab-delimited

please show us what you have written so far. - Rainer Joswig

I haven't written anything yet, My original code is written in Perl and i need to convert it lisp, I don't really know what is the best way to do it. I'm starting to think it may be easier to instead of reading a txt file just to incorporate into the program and then changed it as need be - Lpaulson

2

votes

Try concatenating parentheses onto the front and back of your input string, then using read-from-string (I assume you're using Common Lisp, since you tagged your question clisp).

(setf str "a1   b1      c1      d1      e2")
(print (read-from-string (concatenate 'string "(" str ")")))

2

votes

Yet another way to go about it (a tad more robust, perhaps), You can also easily modify it so that you could `setf' a character in the string once the callback is called, but I didn't do it that way because it seemed like you don't need this sort of ability. Also, in that later case, I'd rather use a macro.

(defun mapc-words (function vector
                  &aux (whites '(#\Space #\Tab #\Newline #\Rubout)))
  "Iterates over string `vector' and calls the `function'
with the non-white characters collected so far.
The white characters are, by default: #\Space, #\Tab
#\Newline and #\Rubout.
`mapc-words' will short-circuit when `function' returns false."
  (do ((i 0 (1+ i))
       (start 0)
       (len 0))
      ((= i (1+ (length vector))))
    (if (or (= i (length vector)) (find (aref vector i) whites))
        (if (> len 0)
            (if (not (funcall function (subseq vector start i)))
                (return-from map-words)
                (setf len 0 start (1+ i)))
            (incf start))
        (incf len))) vector)

(mapc-words
 #'(lambda (word)
     (not
      (format t "word collected: ~s~&" word)))
 "a1     b1     c1     d1     e1
a2     b2     c2     d2     e2")

;; word collected: "a1"
;; word collected: "b1"
;; word collected: "c1"
;; word collected: "d1"
;; word collected: "e1"
;; word collected: "a2"
;; word collected: "b2"
;; word collected: "c2"
;; word collected: "d2"
;; word collected: "e2"

Here's an example macro you could use, if you wanted to modify the string as you read it, but I'm not entirely happy with it, so maybe someone will come up with a better variant.

(defmacro with-words-in-string
    ((word start end
           &aux (whites '(#\Space #\Tab #\Newline #\Rubout)))
     s
     &body body)
  `(do ((,end 0 (1+ ,end))
        (,start 0)
        (,word)
        (len 0))
       ((= ,end (1+ (length ,s))))
     (if (or (= ,end (length ,s)) (find (aref ,s ,end) ',whites))
         (if (> len 0)
             (progn
               (setf ,word (subseq ,s ,start ,end))
               ,@body
               (setf len 0 ,start (1+ ,end)))
             (incf ,start))
         (incf len))))

(with-words-in-string (word start end)
    "a1     b1     c1     d1     e1
a2     b2     c2     d2     e2"
(format t "word: ~s, start: ~s, end: ~s~&" word start end))

0

votes

assuming that they are tabbed (not spaced) then this will create a list

(defun tokenize-tabbed-line (line)
  (loop 
     for start = 0 then (+ space 1)
     for space = (position #\Tab line :start start)
     for token = (subseq line start space)
     collect token until (not space)))

which results in the following:

CL-USER> (tokenize-tabbed-line "a1  b1  c1  d1  e1")
("a1" "b1" "c1" "d1" "e1")

Parse Tab Delimited String

3 Answers