Gauging Interest:RFC to add map() function

Hello Jeremy,

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

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 functionality provided is uncommon but perhaps usefu. However, I am
very against the name map which has a very established meaning in the
programming world; others have already mentioned this but I felt I should
mention it again.

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