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Date: Wed, 26 Jun 2013 08:48:59 -0700
Message-ID: <CALrkBjYKB-01=UomFjCu=aj3beag9zT-5grSrpxC-2Q9T9uxkw@mail.gmail.com>
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: pencap@gmail.com (Mike Willbanks)

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Hello Jeremy,


On Wed, Jun 26, 2013 at 8:20 AM, 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.
>

A map() function is normally part of functional programming and as such
would cause confusion and likely would not mean what most programmers would
assume.  See python and JS docs:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map
http://docs.python.org/2/howto/functional.html

Yes; we do have array_map; but I still do not assume that this would be
a mathematical function.


>
> 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);
> }
>

I am curious with something that is so easy; why would you want it in core?


>
> 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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