reading a file in common lisp

How do i read the following file which has columns of data with header and space or tab delimited, in common lisp.

I also wanted to put the data in to list of list which contains rows.

Also how to get the difference in dates in开发者_C百科 common lisp

ID YR MO DA YrM MoM DaM

100 2010 2 20 2010 8 30

110 2010 4 30 2010 9 12

112 2010 8 20 2010 10 20

The function to read a table with NUMCOLS columns from a stream

It assumes that items from the table can be read with READ. (PEEK-CHAR T ...) tests whether there is still some non-whitespace text in the stream.

(defun read-a-table (stream numcols)
  (cons (loop repeat numcols collect (read stream))
        (loop while (peek-char t stream nil nil)
              collect (loop repeat numcols collect (read stream)))))

Here are two example functions

One reads a table from a file, another one reads a table from a string.

(defun read-a-table-from-file (file numcols)
  (with-open-file (stream file)
    (read-a-table stream numcols)))

(defun read-a-table-from-string (string numcols)
  (with-input-from-string (stream string)
    (read-a-table stream numcols)))

Let's test it with a string:

(defun test ()
  (read-a-table-from-string "ID YR MO DA YrM MoM DaM
100 2010 2 20 2010 8 30
110 2010 4 30 2010 9 12
112 2010 8 20 2010 10 20"
                            7))

Executing the test

CL-USER 15 > (test)

  ((ID YR MO DA YRM MOM DAM)
   (100 2010 2 20 2010 8 30)
   (110 2010 4 30 2010 9 12)
   (112 2010 8 20 2010 10 20))

You can read a full line from a stream with READ-LINE. You use WITH-OPEN-FILE to connect a stream to a file given that you have a filename. To get each line as an element of a list means using LOOP:

(loop
   for line = (read-line stream nil 'eof)
   until (eq line 'eof)
   collect line)

To split each line into columns requires some effort in basic Common Lisp, but there is this cl-utilities package which contains a function called SPLIT-SEQUENCE that can split a delimited string into a list of tokens.

First search for date-handling yielded http://common-lisp.net/project/cl-date-calc/index.html, which has a DELTA-DAYS function.

Use cl-ppcre. The "split" function is perfect for this, and I use it in my programs. Just set it to use a #\Space as the delimiter.