[RESOLVED] Create Colors based on # of Items

[nick1]

Preferably using PHP, I'd like to create X number of colors based on X number of items and using a predefined color range. For example:

ITEM -- VALUE
1 -- 1,234,567,890
2 -- 234,567,890
3 -- 34,567,890
4 -- 4,567,890
5 -- 567,890

Color Range
red = largest value
green = medium value
blue = smallest value

Example
Item 1 gets color red
Item 2 gets whatever color naturally comes between red and green
Item 3 gets color green
Item 4 gets whatever color naturally comes between green and blue
Item 5 gets color blue

Requirements
The code should be able to handle any number of items. 5 items was just an easy example.

Some Thoughts
- Number of items = number of colors
- How to divide a color range into number of items?
- Colors can be represented in decimal format: red=255,000,000 blue=000,000,255
- Can a formula be created, based on the color decimal format, to solve this problem?

I think it's the math portion of the problem that I'm stuck on right now.
Thanks for your help,

Nick

[paulnaj]

Hi Nick,

I've had to do this before myself. You can do this sort of thing ...

<?php
// Given a random list of numbers
$a = array(7890, 1234567890, 234567890, 67890, 890, 34567890, 4567890, 567890, 90);
// Sort decreasing (to match your example)
rsort($a);

$colors = getColors($a); // See function below
foreach($colors as $i => $col){
	echo '<p style="padding: 10px;background-color:'.cssCol($col).'">'.$a[$i].'</p>';
}

function cssCol($col){ return 'rgb('.join(', ', array_values($col)).')'; }
////////////////////////////////////////////////////////
function getColors($a){
	// Get the number of items in the list
	$count = count($a);
	// Find the 'medium' - could be just the 'middle' value, or average, or median
	// Just use middle here
	$middle = ($count - 1)/2; // Note, if count is even then $middle isn't an integer
	$n = ceil($middle);

// Declare an array to store colours
$colors = array();
for($i = 0; $i < $count; $i++){
	$r = $g = $b = 0;
	if($i < $middle){ // mixture of red/green
		$g = $i;
		$r = $n - $g;
	} else if($i > $middle){ // mixture of green/blue
		$b = $i - $n; 
		$g = $n - $b;
	} else { // all green
		$g = $n;
	}
	$colors[$i] = array(
		'r' => floor(255*$r/$n)
	,	'g' => floor(255*$g/$n)
	,	'b' => floor(255*$b/$n)
	);

}
return $colors;
}
////////////////////////////////////////////////////////
?>

There are still things to consider though ...
1. What is your definition of the 'medium' value in a list. The average value might not be the 'middle' value of the array. Another 'medium' could be the median.

2. The order in getColors() is 100% red to 100% green to 100% blue. You could change the order by altering the $r, $g, $b calculations in the if/elseif/else statement.

3. Also, could be extended to other 'boundary' colours, but more the $r, $g, $b calcs would be more involved.

P.

[paulnaj]

Couldn't resist doing 2 and 3 above ...

<?php
// Given a range of three colours ...
$color_range = array(
	array('r' => 255, 'g' => 0, 'b' => 0)
,	array('r' => 0, 'g' => 0, 'b' => 255)
,	array('r' => 0, 'g' => 255, 'b' => 0)
);
// ... and a list of numbers
$a = array(7890, 1234567890, 234567890, 67890, 890, 34567890, 4567890, 567890, 90);

// Sort decreasing (to match your example)
rsort($a);

// Get the array of colours
$colors = getColors($a, $color_range);
foreach($colors as $i => $col){
	echo '
<p style="padding: 10px;background-color:'.cssCol($col).'">'.$a[$i].'</p>';
}

function cssCol($col){ return 'rgb('.join(', ', array_values($col)).')'; }

////////////////////////////////////////////////////////
function getColors($a, $color_range){
	// Get the number of items in the list
	$count = count($a);
	// Find the 'medium' - could be just the 'middle' value, or average, or median
	// Just use middle here
	$middle = ($count - 1)/2; // Note, if count is even then $middle isn't an integer
	$n = ceil($middle);

// Declare an array to store colours
$colors = array();
for($i = 0; $i < $count; $i++){
	$color = array();
	$r = $i < $middle? 0: 1;
	$from = $color_range[$r];
	$to = $color_range[$r + 1];
	$j = $i < $middle? $i: $i - $n;
	foreach($from as $key => $value){
		$color[$key] = floor($from[$key] + $j*($to[$key] - $from[$key])/$n);
	}
	$colors[$i] = $color;
}
return $colors;
}
?>

[nick1]

Thank you for your help! You showed me how to approach the problem from a different view - that's exactly the kind of help I needed. :-)

Nick