Printing the Whole Graph

Now we are nearly ready to print the whole graph.

The function to print the graph with the proper labels follows the outline we created earlier (see section A Graph with Labelled Axes), but with additions.

Here is the outline:

(defun print-graph (numbers-list)
  "documentation..."
  (let ((height  ...
        ...))
    (print-Y-axis height ... )
    (graph-body-print numbers-list)
    (print-X-axis ... )))

The final version is different from what we planned in two ways: first, it contains additional values calculated once in the varlist; second, it carries an option to specify the labels' increment per row. This latter feature turns out to be essential; otherwise a graph may have more rows than fit on a display or on a sheet of paper.

This new feature requires a change to the Y-axis-column function, to add vertical-step to it. The function looks like this:

;;; Final version.
(defun Y-axis-column
  (height width-of-label &optional vertical-step)
  "Construct list of labels for Y axis.
HEIGHT is maximum height of graph.  
WIDTH-OF-LABEL is maximum width of label.
VERTICAL-STEP, an option, is a positive integer 
that specifies how much a Y axis label increments 
for each line.  For example, a step of 5 means 
that each line is five units of the graph."
  (let (Y-axis
        (number-per-line (or vertical-step 1)))
    (while (> height 1)
      (if (zerop (% height Y-axis-label-spacing))
          ;; Insert label.
          (setq Y-axis
                (cons
                 (Y-axis-element
                  (* height number-per-line)
                  width-of-label)
                 Y-axis))
        ;; Else, insert blanks.
        (setq Y-axis
              (cons
               (make-string width-of-label ? )
               Y-axis)))
      (setq height (1- height)))
    ;; Insert base line.
    (setq Y-axis (cons (Y-axis-element 
                        (or vertical-step 1)
                        width-of-label)
                       Y-axis))
    (nreverse Y-axis)))

The values for the maximum height of graph and the width of a symbol are computed by print-graph in its let expression; so graph-body-print must be changed to accept them.

;;; Final version.
(defun graph-body-print (numbers-list height symbol-width)
  "Print a bar graph of the NUMBERS-LIST.
The numbers-list consists of the Y-axis values.
HEIGHT is maximum height of graph.
SYMBOL-WIDTH is number of each column."
  (let (from-position)
    (while numbers-list
      (setq from-position (point))
      (insert-rectangle
       (column-of-graph height (car numbers-list)))
      (goto-char from-position)
      (forward-char symbol-width)
      ;; Draw graph column by column.
      (sit-for 0)               
      (setq numbers-list (cdr numbers-list)))
    ;; Place point for X axis labels.
    (forward-line height)
    (insert "\n")))

Finally, the code for the print-graph function:

;;; Final version.
(defun print-graph
  (numbers-list &optional vertical-step)
  "Print labelled bar graph of the NUMBERS-LIST.
The numbers-list consists of the Y-axis values.

Optionally, VERTICAL-STEP, a positive integer,
specifies how much a Y axis label increments for
each line.  For example, a step of 5 means that
each row is five units."
  (let* ((symbol-width (length graph-blank))
         ;; height is both the largest number
         ;; and the number with the most digits.
         (height (apply 'max numbers-list))
         (height-of-top-line
          (if (zerop (% height Y-axis-label-spacing))
              height
            ;; else
            (* (1+ (/ height Y-axis-label-spacing))
               Y-axis-label-spacing)))
         (vertical-step (or vertical-step 1))
         (full-Y-label-width
          (length
           (concat
            (int-to-string
             (* height-of-top-line vertical-step))
            Y-axis-tic))))

    (print-Y-axis
     height-of-top-line full-Y-label-width vertical-step)
    (graph-body-print
     numbers-list height-of-top-line symbol-width)
    (print-X-axis numbers-list)))

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