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Date: Thu, 27 Jun 2013 17:17:24 +0800
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To: Florin Patan <florinpatan@gmail.com>
Cc: Jeremy Curcio <j.curcio@icloud.com>, 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 Thu, Jun 27, 2013 at 4:27 PM, Florin Patan <florinpatan@gmail.com> wrote:

> On Thu, Jun 27, 2013 at 10:17 AM, Tjerk Anne Meesters <datibbaw@php.net>
> wrote:
> > 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
> >>
> >
> >
> >
> > --
> > --
> > Tjerk
>
>
> Hi,
>
>
> May I kindly ask why all the PHP users would want this function in the
> core?
>

Are you meaning to ask why would *any* php user want this function in the
core? As with most things, the need of one may be shared among a critical
mass that could swing the balance. In practice though, the critical mass is
usually determined by the internals peeps :)


> I've never needed such a function nor do I understand why we should
> have it. It's good for what?
>

It's good to perform affine transformation in a single dimension; if you've
never done this before, you wouldn't need it.


> And as I understand, PHP delegates the math stuff to the underlying C
> implementation so why would it be faster having it in PHP core rather
> that in PHP userland?
>

Performance is not the only reason why features make it into the core; it's
providing a rich set of built-in features to make the developer's lives
easier, such as the latest password hashing API which is easy to get wrong
or generators that reduce boiler plate code. As such, an addition to the
set of numerical functions to address a particular use-case is not
unthinkable.


>
>
> Thanks
> ----
> Florin Patan
> https://github.com/dlsniper
> http://www.linkedin.com/in/florinpatan
>



-- 
--
Tjerk

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