PHP 8.4.1 Released!

    stats_stat_percentile

    (PECL stats >= 1.0.0)

    stats_stat_percentile — Renvoie la valeur du centile

    Description

    stats_stat_percentile(array $arr, float $perc): float

    Renvoie la valeur du perc-ième centile de l'ensemble de données arr.

    Liste de paramètres

    arr

    Le tableau d'entrée

    perc

    Le centile

    Valeurs de retour

    Renvoie le centile de l'ensemble de données.

    Improve This Page

    Learn How To Improve This Page • Submit a Pull Request • Report a Bug
    ＋add a note

    User Contributed Notes 2 notes

    up
    8
    aboulang2002 at yahoo dot com
    15 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.]
    up
    4
    yuvaraj dot v at gmail dot com
    16 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
    ＋add a note
    To Top