[PATCH] partial rewrite of gnuplot-to-grid-data

[Mario Frasca <mario@anche.no>]

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according to me, this looks better, I'm curious about the reactions from 
the list.

in particular, I was surprised finding a duplicated evaluation of 
(string-to-number (nth col (nth row table))) inside a (dotimes (col 
num-cols) (dotimes (row num-rows) …))



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From 9822748dfbdb99f1ea534e695e818d7533920a61 Mon Sep 17 00:00:00 2001
From: mfrasca <mario@anche.no>
Date: Sun, 28 Jun 2020 16:24:54 -0500
Subject: [PATCH] org-plot/gnuplot-to-grid-data: code review for speed and
 readability

* lisp/org-plot.el (org-plot/gnuplot-to-grid-data): partial rewrite.

Optimizing for speed and readability: preprocessing data in order to
simplify removal on non-plotting columns; using available functions
like set-difference and org-remove-by-index; loop over elements
instead of counting indices and invoking `nth' (in a double loop).
---
 lisp/org-plot.el | 81 +++++++++++++++++++++---------------------------
 1 file changed, 36 insertions(+), 45 deletions(-)

diff --git a/lisp/org-plot.el b/lisp/org-plot.el
index bf81d3c37..38749c069 100644
--- a/lisp/org-plot.el
+++ b/lisp/org-plot.el
@@ -130,53 +130,44 @@ Pass PARAMS through to `orgtbl-to-generic' when exporting TABLE."
 (defun org-plot/gnuplot-to-grid-data (table data-file params)
   "Export the data in TABLE to DATA-FILE for gnuplot.
 This means in a format appropriate for grid plotting by gnuplot.
-PARAMS specifies which columns of TABLE should be plotted as independent
-and dependent variables."
-  (interactive)
-  (let* ((ind (- (plist-get params :ind) 1))
-	 (deps (if (plist-member params :deps)
-		   (mapcar (lambda (val) (- val 1)) (plist-get params :deps))
-		 (let (collector)
-		   (dotimes (col (length (nth 0 table)))
-		     (setf collector (cons col collector)))
-		   collector)))
-	 (counter 0)
-	 row-vals)
-    (when (>= ind 0) ;; collect values of ind col
-      (setf row-vals (mapcar (lambda (row) (setf counter (+ 1 counter))
-			       (cons counter (nth ind row)))
-			     table)))
-    (when (or deps (>= ind 0)) ;; remove non-plotting columns
-      (setf deps (delq ind deps))
-      (setf table (mapcar (lambda (row)
-			    (dotimes (col (length row))
-			      (unless (memq col deps)
-				(setf (nth col row) nil)))
-			    (delq nil row))
-			  table)))
+PARAMS specifies which columns of TABLE should be plotted as
+independent and dependent variables.  Return the ind-column, as
+list of (cons 0-based-row-num . cell-value)."
+  (let* ((last-col (1- (length (car table))))
+         (ind (1- (plist-get params :ind)))
+         (deps (delq ind (if (plist-member params :deps)
+                             (mapcar #'1- (plist-get params :deps))
+                           (number-sequence 0 last-col))))
+         (skip-deps (set-difference
+                     (number-sequence 0 last-col)
+                     deps))
+         (row-vals ; the return value - indexed values from the ind column
+          (unless (< ind 0)
+            (let ((i -1)) (mapcar (lambda (row)
+                                    (incf i)
+                                    (cons i (nth ind row)))
+                                  table)))))
+    ;; remove non-plotting columns
+    (setq table (mapcar (lambda (row) 
+                          (org-remove-by-index row skip-deps))
+                        table))
     ;; write table to gnuplot grid datafile format
     (with-temp-file data-file
-      (let ((num-rows (length table)) (num-cols (length (nth 0 table)))
-	    (gnuplot-row (lambda (col row value)
-			   (setf col (+ 1 col)) (setf row (+ 1 row))
-			   (format "%f  %f  %f\n%f  %f  %f\n"
-				   col (- row 0.5) value ;; lower edge
-				   col (+ row 0.5) value))) ;; upper edge
-	    front-edge back-edge)
-	(dotimes (col num-cols)
-	  (dotimes (row num-rows)
-	    (setf back-edge
-		  (concat back-edge
-			  (funcall gnuplot-row (- col 1) row
-				   (string-to-number (nth col (nth row table))))))
-	    (setf front-edge
-		  (concat front-edge
-			  (funcall gnuplot-row col row
-				   (string-to-number (nth col (nth row table)))))))
-	  ;; only insert once per row
-	  (insert back-edge) (insert "\n") ;; back edge
-	  (insert front-edge) (insert "\n") ;; front edge
-	  (setf back-edge "") (setf front-edge ""))))
+      (let ((gnuplot-row (lambda (c r value)
+                           (format "%f  %f  %s\n%f  %f  %s\n"
+                                   c (+ r 0.5) value
+                                   c (+ r 1.5) value))))
+        (dotimes (c (length (car table)))
+          (let ((column (mapcar (lambda (row) (nth c row)) table))
+                (r 0)
+                front-edge back-edge)
+            (dolist (cell column)
+              (setq back-edge (concat back-edge
+                                      (funcall gnuplot-row c r cell)))
+              (setq front-edge (concat front-edge
+                                       (funcall gnuplot-row (1+ c) r cell)))
+              (incf r))
+            (insert (concat back-edge "\n" front-edge "\n"))))))
     row-vals))
 
 (defun org-plot/gnuplot-script (data-file num-cols params &optional preface)
-- 
2.20.1