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Date: Thu, 27 Jun 2013 16:17:01 +0800
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To: Jeremy Curcio <j.curcio@icloud.com>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Gauging Interest:RFC to add map() function
From: datibbaw@php.net (Tjerk Anne Meesters)

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On Wed, Jun 26, 2013 at 11:20 PM, Jeremy Curcio <j.curcio@icloud.com> wrote:

> Hello,
>
> I would like to submit an RFC to add a new function to the PHP language.
> The function would be called "map()". The purpose of this function would be
> to take an existing value within a range and make it to a corresponding
> location within a new range.
>
> The map() method would have 5 required parameters, $originalLow,
> $originalHigh, $newLow, $newHigh, and $value.
>
> map() would be implement the following:
>
> function map($originalLow, $originalHigh, $newLow, $newHigh, $value) {
> return $newLow + ($value - $originalLow) * ($newHigh - $newLow) /
> ($originalHigh- $originalLow);
> }
>
>
Purely from a development perspective, having five required function
arguments is bad; it can be reduced (by treating the first four as two
ranges) to three arguments, e.g.

    map([55, 92], [70, 100], 55);

You can go one step further and call it what it is, not a mapper, but a
single dimensional range transformer and use a closure, e.g.:

    $transformer = get_1d_range_transformer([55, 92], [70, 100]);
    echo $transformer(55); // get transformed value

You might also benefit from an OOP approach. I won't paste it here, but
I've created a pastie for it: http://codepad.org/nGZv8GJa

It's debatable whether this somewhat specialized code would need to be
coded at something other than the language level; in most likelihood you
won't gain any appreciable performance increase.


> Example:
> Let's say we are teachers and are grading final exams. We have a policy
> that the best score is 100, and the worst score is a 70. Students scored
> between 55 and 92. We want to easily re-score the exams to be within the
> new score range, so we would use the new map() function. Let's begin with
> mapping the lowest score:
>
> $newScore = map(55, 92, 70, 100, 55); //$newScore = 70
>
> If we have all of our scores in an array:
>
> $scores = array(71, 65, 55, 85, 88, 86, 92, 77, 73);
>
> We could use a foreach loop to remap each value:
>
> $newScores = array();
> foreach($score as $scores) {
>  $newScores[] = map(55, 92, 70, 100, $score);
> }
> var_dump($newScores);
> /*
> array(9) {
>   [0]=>
>   float(82.972972972973)
>   [1]=>
>   float(78.108108108108)
>   [2]=>
>   int(70)
>   [3]=>
>   float(94.324324324324)
>   [4]=>
>   float(96.756756756757)
>   [5]=>
>   float(95.135135135135)
>   [6]=>
>   int(100)
>   [7]=>
>   float(87.837837837838)
>   [8]=>
>   float(84.594594594595)
>   }
> */
>
> Just like that, we have the new exam grades that fit our policy, within
> the proper scale, without having to do any of the messy math ourselves.
>
> While I do recognize that this is somewhat trivial to anyone who knows the
> proper formula, I feel as though it would serve the PHP community well.
> Much the same as the pow() or pi() functions do. I appreciate your thoughts
> on this matter and whether or not this is worth pursuing as an RFC.
>
> Thank you,
> Jeremy Curcio
> j.curcio@me.com
>



-- 
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Tjerk

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