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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.lisp
Subject: Re: matrix operations
Date: Wed, 3 Jul 2024 02:41:20 -0000 (UTC)
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On 2024-07-03, B. Pym <No_spamming@noWhere_7073.org> wrote:
> Barry Margolin wrote:
>
>> Zachary Turner <ztur...@bindview.com> wrote: 
>> >I've got a 3x3 matrix, stored as ((r1c1 r1c2 r1c3) (r2c1 r2c2 r2c3) (r3c1 
>> >r3c2 r3c3)).  I want to check if any of the columns have the same three 
>> >elements.  It's easy for rows, I can just use 
>> >(or 
>> >   (every #'equal (car matrix)) 
>> >   (every #'equal (cadr matrix)) 
>> >   (every #'equal (caddr matrix))) 
>> 

If it didn't have to scale to larger matrices, I'd probaby just do:

(defun has-column-3x3 (matrix)
  (if-match @(or ((@x . @nil)
                  (@x . @nil)
                  (@x . @nil))
                 ((@nil @x . @nil)
                  (@nil @x . @nil)
                  (@nil @x . @nil))
                 ((@nil @nil @x)
                  (@nil @nil @x)
                  (@nil @nil @x)))
            matrix
    t))

(defun has-column-3x3 (matrix)
  (if-match @(or ((@x @x @xl) . @nil)
                 (@nil (@x @x @x) . @nil)
                 (@nil @nil (@x @x @x)))
            matrix
    t))

(defun has-diagonal-3x3 (matrix)
  (if-match @(or ((@x . @nil)
                  (@nil @x . @nil)
                  (@nil @nil @x))
                 ((@nil @nil @x)
                  (@nil @x . @nil)
                  (@x . @nil)))
            matrix
    t))

If we want to test for a specific value of x (e.g. #\X or #\O
in Tic Tac Toe), we just add that as a parameter

(defun has-diagonal-3x3 (matrix x)
  (if-match @(or ((@x . @nil)
                  (@nil @x . @nil)
                  (@nil @nil @x))
                 ((@nil @nil @x)
                  (@nil @x . @nil)
                  (@x . @nil)))
            matrix
    t))

The pattern matcher will substitute the value of the existing
lexical x for the pattern variable @x.

2> (has-diagonal-3x3 '((x o o)
                       (o x _)
                       (_ _ x)) 'x)
t
3> (has-diagonal-3x3 '((x o o)
                       (o _ _)
                       (_ _ x)) 'x)
nil
4> (has-diagonal-3x3 '((x o o)
                       (o o x)
                       (o x x)) 'x)
nil
5> (has-diagonal-3x3 '((x o o)
                       (o o x)
                       (o x x)) 'o)
t

Backquote notation can be used.

(defun has-diagonal-3x3 (matrix x)
  (if-match @(or ^((,x . ,nil)
                   (,nil ,x . ,nil)
                   (,nil ,nil ,x))
                 ^((,nil ,nil ,x)
                   (,nil ,x . ,nil)
                   (,x . ,nil)))
            matrix
    t))

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
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