2013/6/27 Tjerk Anne Meesters <datib...@php.net>
> On Thu, Jun 27, 2013 at 4:27 PM, Florin Patan <florinpa...@gmail.com>
> wrote:
>
> > On Thu, Jun 27, 2013 at 10:17 AM, Tjerk Anne Meesters <datib...@php.net>
> > wrote:
> > > On Wed, Jun 26, 2013 at 11:20 PM, Jeremy Curcio <j.cur...@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.cur...@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 :)
>
But this method is _really_ quite special, isn't it? I cannot imagine, that
there is "critical mass", that needs this _in core_.
Just to remind: It works with pure-PHP too. Also you may provide this as
PECL-extension if performance is important.
>
>
> > 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.
You cannot compare language features (generators) with functions. And
"security" is always a topic on its own.
> 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
>
--
github.com/KingCrunch
