PHP 5.5.16 is released

stats_stat_percentile

(PECL stats >= 1.0.0)

stats_stat_percentileNot documented

Descrizione

float stats_stat_percentile ( float $df , float $xnonc )
Avviso

Questa funzione, al momento non è documentata; è disponibile soltanto la lista degli argomenti.

Elenco dei parametri

df

xnonc

Valori restituiti

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User Contributed Notes 2 notes

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2
yuvaraj dot v at gmail dot com
6 years ago
I have looked at the code available in the Math package for percentile. I compared the result obtained with percentile from Excel and found that it doesnt match. So i wrote my own percentile function and verified the result with the Excel's percentile.

For those of you who need the percentile calculation of Excel in php..

<?php
function mypercentile($data,$percentile){
    if(
0 < $percentile && $percentile < 1 ) {
       
$p = $percentile;
    }else if(
1 < $percentile && $percentile <= 100 ) {
       
$p = $percentile * .01;
    }else {
        return
"";
    }
   
$count = count($data);
   
$allindex = ($count-1)*$p;
   
$intvalindex = intval($allindex);
   
$floatval = $allindex - $intvalindex;
   
sort($data);
    if(!
is_float($floatval)){
       
$result = $data[$intvalindex];
    }else {
        if(
$count > $intvalindex+1)
           
$result = $floatval*($data[$intvalindex+1] - $data[$intvalindex]) + $data[$intvalindex];
        else
           
$result = $data[$intvalindex];
    }
    return
$result;
}
?>

The above code may not be elegant.. but it solves my problem..

yuvaraj
up
1
aboulang2002 at yahoo dot com
5 years ago
If you are looking to infer the percentile from a z-score, you can use this function.
It's far from precise but does the job on most circumstances.
The error function ( erf() )is based on the approximation on wikipedia:
http://en.wikipedia.org/wiki/Error_function

<?php
function erf($x)
{
       
$pi = 3.1415927;
       
$a = (8*($pi - 3))/(3*$pi*(4 - $pi));
       
$x2 = $x * $x;

       
$ax2 = $a * $x2;
       
$num = (4/$pi) + $ax2;
       
$denom = 1 + $ax2;

       
$inner = (-$x2)*$num/$denom;
       
$erf2 = 1 - exp($inner);

        return
sqrt($erf2);
}

function
cdf($n)
{
        if(
$n < 0)
        {
                return (
1 - erf($n / sqrt(2)))/2;
        }
        else
        {
                return (
1 + erf($n / sqrt(2)))/2;
        }
}

// EXAMPLE
$sample = 90;
$avg = 75;
$stddev = 12;

$zscore = ($sample - $avg) / $stddev;
print
'Percentile: ' . cdf($zscore) * 100 . "\n";
?>

Where $n is the z-score

The function cdf() returns the approximed cumulative standard normal distribution ([0..1])



[EDIT BY danbrown AT php DOT net: Contains a bugfix provided by (Ed) on 24-FEB-2010 which fixes the definition of $a in erf() with the note that it is "out by a factor of -1" in the original code.]
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