how to create "pretty" numbers? - php

Question

my question is: is there a good (common) algorithm to create numbers, which match well looking user understood numbers out of incomming (kind of random looking for a user) numbers.
i.e. you have an interval from
130'777.12 - 542'441.17.
But for the user you want to display something more ...say userfriendly, like:
130'000 - 550'000.
how can you do this for several dimensions?
an other example would be:
23.07 - 103.50 to 20 - 150
do you understand what i mean?
i should give some criteria as well:
the interval min and max should
include the given limits.
the "rounding" should be in a
granularity which reflects the
distance between min and max (meaning
in our second example 20 - 200
would be too coarse)
very much honor you'll earn if you know a native php function which can do this :-)
*update - 2011-02-21 *
I like the answer from #Ivan and so accepted it. Here is my solution so far:
maybe you can do it better. i am open for any proposals ;-).
/**
* formats a given float number to a well readable number for human beings
* #author helle + ivan + greg
* #param float $number
* #param boolean $min regulates wheter its the min or max of an interval
* #return integer
*/
function pretty_number($number, $min){
$orig = $number;
$digit_count = floor(log($number,10))+1; //capture count of digits in number (ignoring decimals)
switch($digit_count){
case 0: $number = 0; break;
case 1:
case 2: $number = round($number/10) * 10; break;
default: $number = round($number, (-1*($digit_count -2 )) ); break;
}
//be sure to include the interval borders
if($min == true && $number > $orig){
return pretty_number($orig - pow(10, $digit_count-2)/2, true);
}
if($min == false && $number < $orig){
return pretty_number($orig + pow(10, $digit_count-2)/2, false);
}
return $number;
}

Answer 1

I would use Log10 to find how "long" the number is and then round it up or down. Here's a quick and dirty example.
echo prettyFloor(23.07);//20
echo " - ";
echo prettyCeil(103.50);//110
echo prettyFloor(130777.12);//130000
echo " - ";
echo prettyCeil(542441.17);//550000
function prettyFloor($n)
{
$l = floor(log(abs($n),10))-1; // $l = how many digits we will have to nullify :)
if ($l<=0)
$l++;
if ($l>0)
$n=$n/(pow(10,$l)); //moving decimal point $l positions to the left eg(if $l=2 1234 => 12.34 )
$n=floor($n);
if ($l>0)
$n=$n*(pow(10,$l)); //moving decimal point $l positions to the right eg(if $l=2 12.3 => 1230 )
return $n;
}
function prettyCeil($n)
{
$l = floor(log(abs($n),10))-1;
if ($l<=0)
$l++;
if ($l>0)
$n=$n/(pow(10,$l));
$n=ceil($n);
if ($l>0)
$n=$n*(pow(10,$l));
return $n;
}
This example unfortunately will not convert 130 to 150. As both 130 and 150 have the same precision. Even thou for us, humans 150 looks a bit "rounder". In order to achieve such result I would recommend to use quinary system instead of decimal.

Answer 2

You can use php's round function which takes a parameter to specify the precision.
<?php
echo round(3.4); // 3
echo round(3.5); // 4
echo round(3.6); // 4
echo round(3.6, 0); // 4
echo round(1.95583, 2); // 1.96
echo round(1241757, -3); // 1242000
echo round(5.045, 2); // 5.05
echo round(5.055, 2); // 5.06
?>

Answer 3

The number_format() function handles "prettifying" numbers with arbitrary thousands/decimal characters and decimal places, but you'd have to split your ranges/strings into individual numbers, as number_formation only works on one number at a time.
The rounding portion would have to handled seperately as well.

Answer 4

I haven't seen ready algorithm or function for that. But it should be simple, based on string replacement (str_replace, preg_replace), number_format and round functions.

Answer 5

This actually is kind of a special case, that can be addressed with the following function:
function roundto($val, $toceil=false) {
$precision=2; // try 1, 2, 5, 10
$pow = floor(log($val, 10));
$mult = pow(10, $pow);
$a = $val/$mult*$precision;
if (!$toceil) $a-=0.5; else $a+=0.5;
return round($a)/$precision*$mult;
}
$v0=130777.12; $v1=542441.17;
echo number_format(roundto($v0, false), 0, '.', "'").' - '
.number_format(roundto($v1, true), 0, '.', "'").'<br/>';
$v0=23.07; $v1=103.50;
echo number_format(roundto($v0, false), 0, '.', "'").' - '
.number_format(roundto($v1, true), 0, '.', "'").'<br/>';
Outputs exactly this:
100'000 - 550'000
20 - 150
For any other case of number formatting it might be interesting to have a look at my newly published PHP class "php-beautiful-numbers", which I use in almost ever project to display run times ("98.4 µs" [= 9.8437291615846E-5]) or numbers in running text (e.g. "you booked two flights." [= 2]).
https://github.com/SirDagen/php-beautiful-numbers