Re: Trade-off, option, choice.

verec wrote: 
I've got a two dimensional grid of characters.

At one stage, I need to extract strings from the grid,
either on a row by row basis, or on a column by column
basis.


[...]

Anyone see any other options I missed?

I' m a big fan of (1) the :displaced-to feature of <make-array>, and (2) <loop>.

Carl Taylor


(defun get-char-grid-row (row x-grid)
 (declare (type fixnum row))
 (let ((col-cnt (array-dimension x-grid 1)))
    (map 'string #'identity
      (make-array col-cnt
                           :element-type (array-element-type x-grid)
                           :displaced-to x-grid
                           :displaced-index-offset (* row col-cnt)))))


(defun get-char-grid-col (col x-grid)
 (declare (type fixnum col))
 (map 'string #'identity
    (loop :for i fixnum
              :repeat (the fixnum (array-dimension x-grid 0))
              :collect (aref x-grid i col))))


CL-USER 13 >
(get-char-grid-row 2 #2A((#\a #\b #\c) (#\d #\e #\f) (#\g #\h #\i)))
"ghi"

CL-USER 14 >

(get-char-grid-col 1 #2A((#\a #\b #\c) (#\d #\e #\f) (#\g #\h #\i)))
"beh"







.