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(emacs-lisp-intro.info)Y Axis Element

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Enter node , (file) or (file)node

Construct a Y Axis Element
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   When we print the vertical axis, we want to insert strings such as
`5 -' and `10 - ' every five lines.  Moreover, we want the numbers and
dashes to line up, so shorter numbers must be padded with leading
spaces.  If some of the strings use two digit numbers, the strings with
single digit numbers must include a leading blank space before the
number.

   To figure out the length of the number, the `length' function is
used.  But the `length' function works only with a string, not with a
number.  So the number has to be converted from being a number to being
a string.  This is done with the `number-to-string' function.  For
example,

     (length (number-to-string 35))
          => 2
     
     (length (number-to-string 100))
          => 3

(`number-to-string' is also called `int-to-string'; you will see this
alternative name in various sources.)

   In addition, in each label, each number is followed by a string such
as ` - ', which we will call the `Y-axis-tic' marker.  This variable is
defined with `defvar':

     (defvar Y-axis-tic " - "
        "String that follows number in a Y axis label.")

   The length of the Y label is the sum of the length of the Y axis tic
mark and the length of the number of the top of the graph.

     (length (concat (number-to-string height) Y-axis-tic)))

   This value will be calculated by the `print-graph' function in its
varlist as `full-Y-label-width' and passed on.  (Note that we did not
think to include this in the varlist when we first proposed it.)

   To make a complete vertical axis label, a tic mark is concatenated
with a number; and the two together may be preceded by one or more
spaces depending on how long the number is.  The label consists of
three parts: the (optional) leading spaces, the number, and the tic
mark.  The function is passed the value of the number for the specific
row, and the value of the width of the top line, which is calculated
(just once) by `print-graph'.

     (defun Y-axis-element (number full-Y-label-width)
       "Construct a NUMBERed label element.
     A numbered element looks like this `  5 - ',
     and is padded as needed so all line up with
     the element for the largest number."
       (let* ((leading-spaces
              (- full-Y-label-width
                 (length
                  (concat (number-to-string number)
                          Y-axis-tic)))))
         (concat
          (make-string leading-spaces ? )
          (number-to-string number)
          Y-axis-tic)))

   The `Y-axis-element' function concatenates together the leading
spaces, if any; the number, as a string; and the tic mark.

   To figure out how many leading spaces the label will need, the
function subtracts the actual length of the label--the length of the
number plus the length of the tic mark--from the desired label width.

   Blank spaces are inserted using the `make-string' function.  This
function takes two arguments: the first tells it how long the string
will be and the second is a symbol for the character to insert, in a
special format.  The format is a question mark followed by a blank
space, like this, `? '.  Note: Character Type,
for a description of the syntax for characters.

   The `number-to-string' function is used in the concatenation
expression, to convert the number to a string that is concatenated with
the leading spaces and the tic mark.