A percentile function for PowerShell

Get-Percentile.ps1

# MIT License

# Copyright (c) 2022 Jim Birley

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.


function Get-Percentile {

<#
.SYNOPSIS
    Returns the specified percentile value for a given set of numbers.
 
.DESCRIPTION
    This function expects a set of numbers passed as an array to the 'Sequence' parameter.  For a given percentile, passed as the 'Percentile' argument,
    it returns the calculated percentile value for the set of numbers.
 
.PARAMETER Sequence
    A array of integer and/or decimal values the function uses as the data set.

.PARAMETER Percentile
    The target percentile to be used by the function's algorithm. 
 
.EXAMPLE
    $values = 98.2,96.5,92.0,97.8,100,95.6,93.3
    Get-Percentile -Sequence $values -Percentile 0.95
 
.NOTES
    Author:  Jim Birley
#>

    [CmdletBinding()]
    param (
        [Parameter(Mandatory)] 
        [Double[]]$Sequence
        ,
        [Parameter(Mandatory)]
        [Double]$Percentile
    )
   
    $Sequence = $Sequence | Sort-Object
    [int]$N = $Sequence.Length
    Write-Verbose "N is $N"
    [Double]$Num = ($N - 1) * $Percentile + 1
    Write-Verbose "Num is $Num"
    if ($num -eq 1) {
        return $Sequence[0]
    } elseif ($num -eq $N) {
        return $Sequence[$N-1]
    } else {
        $k = [Math]::Floor($Num)
        Write-Verbose "k is $k"
        [Double]$d = $num - $k
        Write-Verbose "d is $d"
        return $Sequence[$k - 1] + $d * ($Sequence[$k] - $Sequence[$k - 1])
    }
}

Thanks for this function. What is the license for it? Can you mark it with one? Thanks.

I have added an MIT license to this Gist. Thanks for inquiring.

This is awesome! Thanks, @jbirley. Used it to generate some metrics to measure percentiles for client upload file sizes.