Get all combinations of an array

Question

I'm currently trying to make a function that gets all possible combinations of array values.

I have come up with a non function version but it's limited to 3 values so i'm trying to make a function out of it to become more Dynamic

I tried searching SO but could not find a powershell example of what i was trying to do, i could find a PHP version but i'm very limited in my PHP

PHP: How to get all possible combinations of 1D array?

Non-function Script

$name = 'First','Middle','Last'

$list = @()

foreach ($c1 in $name) {
    foreach ($c2 in $name) {
        foreach ($c3 in $name) {
            if (($c1 -ne $c2) -and ($c2 -ne $c3) -and ($c3 -ne $c1))
            {
                $list += "$c1 $c2 $c3"
            }
        }
    }
}

This gives me the result

First Middle Last
First Last Middle
Middle First Last
Middle Last First
Last First Middle
Last Middle First

I'm not sure how i would rearrange the values when i'm recursing the function, this is what i have so far:

<#
.Synopsis
    Short description
.DESCRIPTION
    Long description
.EXAMPLE
    Example of how to use this cmdlet
.EXAMPLE
    Another example of how to use this cmdlet
#>
function Get-Combinations
{
    [CmdletBinding()]
    [OutputType([int])]
    Param
    (
        # Param1 help description
        [Parameter(Mandatory=$true,
                   ValueFromPipelineByPropertyName=$true,
                   Position=0)]
        [string[]]$Array,

        # Param1 help description
        [Parameter(Mandatory=$false,
                   ValueFromPipelineByPropertyName=$false,
                   Position=1)]
        [string]$Temp,

        # Param1 help description
        [Parameter(Mandatory=$false,
                   ValueFromPipelineByPropertyName=$true,
                   Position=2)]
        [string[]]$Return
    )

    Begin
    {
        Write-Verbose "Starting Function Get-Combinations with parameters `n`n$($Array | Out-String)`n$temp`n`n$($Return | Out-String)"

        If ($Temp)
        {
            $Return = $Temp
        }

        $newArray = new-object system.collections.arraylist
    }
    Process
    {
        Write-Verbose ($return | Out-String)

        For($i=0; $i -lt $Array.Length; $i++)
        {
            #Write-Verbose $i

            $Array | ForEach-Object {$newArray.Add($_)}
            $newArray.RemoveAt($i)

            Write-Verbose ($newArray | Out-String)

            if ($newArray.Count -le 1)
            {
                Get-Combinations -Array $newArray -Temp $Temp -Return $Return
            }
            else
            {
                $Return = $Temp
            }
        }
        $newArray
    }
    End
    {
        Write-Verbose "Exiting Function Get-Combinations"
    }
}

$combinations = @("First","First2","Middle","Last")

$Combos = Get-Combinations -Array $combinations

$Combos

But the output i'm getting is all over the place

First2
Last
First2
Last
First
First2
Middle
Last
First
First2
Middle
Last

28/08 Update

Getting closer but still getting weird output

<#
.Synopsis
    Short description
.DESCRIPTION
    Long description
.EXAMPLE
    Example of how to use this cmdlet
.EXAMPLE
    Another example of how to use this cmdlet
#>
function Get-Combinations
{
    [CmdletBinding()]
    [OutputType([int])]
    Param
    (
        # Param1 help description
        [Parameter(Mandatory=$true,
                    ValueFromPipelineByPropertyName=$true,
                    Position=0)]
        [string[]]$Array,

        # Param1 help description
        [Parameter(Mandatory=$false,
                    ValueFromPipelineByPropertyName=$false,
                    Position=1)]
        [string]$Temp,

        # Param1 help description
        [Parameter(Mandatory=$false,
                    ValueFromPipelineByPropertyName=$true,
                    Position=2)]
        [string[]]$Return
    )

    Begin
    {
        Write-Verbose "Starting Function Get-Combinations with parameters `n`n$($Array | Out-String)`n$temp`n`n$($Return | Out-String)"

        If ($Temp)
        {
            $Return += $Temp
        }

        #$newArray = new-object [System.Collections.ArrayList]
        #$Array | ForEach-Object {$newArray.Add($_) | Out-Null}

        [System.Collections.ArrayList]$newArray = $Array
    }
    Process
    {
        Write-Verbose "return -> $return"

        For($i=0; $i -lt $Array.Length; $i++)
        {
            Write-Verbose "`$i -> $i"

            $element = $newArray[0]
            $newArray.RemoveAt(0)

            Write-Verbose "`$newArray -> $newArray"
            Write-Verbose "Element -> $element"

            if ($newArray.Count -gt 0)
            {
                Get-Combinations -Array $newArray -Temp (($temp + " " +$element).Trim()) -Return $Return
            }
            else
            {
                $Return = $Temp + " " + $element
            }
        }
        $return
    }
    End
    {
        Write-Verbose "Exiting Function Get-Combinations"
    }
}

$combinations = @("First","First2","Middle","Last")

$return = @()

$Combos = Get-Combinations -Array $combinations -Return $return

$Combos

New output (Yes there is a space before the 'Last' value, no i have no idea why)

First First2 Middle Last
First First2 Last
First Middle Last
First Last
First2 Middle Last
First2 Last
Middle Last
 Last

So you want to include 1..$arr.count results? Such as 'First' being valid, as well as 'First, First2' and 'First, First2, Middle' and 'First, First2, Middle, Last' and all combinations there of. Is that correct? — TheMadTechnician, Aug 28 '14 at 15:41

David Brabant · Accepted Answer · 2014-08-28T11:52:13.230

Here is my solution:

function Remove ($element, $list)
{
    $newList = @()
    $list | % { if ($_ -ne $element) { $newList += $_} }

    return $newList
}


function Append ($head, $tail)
{
    if ($tail.Count -eq 0)
        { return ,$head }

    $result =  @()

    $tail | %{
        $newList = ,$head
        $_ | %{ $newList += $_ }
        $result += ,$newList
    }

    return $result
}


function Permute ($list)
{
    if ($list.Count -eq 0)
        { return @() }

    $list | %{
        $permutations = Permute (Remove $_ $list)
        return Append $_ $permutations
    }
}

cls

$list = "x", "y", "z", "t", "v"

$permutations = Permute $list


$permutations | %{
    Write-Host ([string]::Join(", ", $_))
}

EDIT: the same in one function (Permute). This is cheating a bit, however since I replaced plain functions whith lambdas. You could replace recursive calls with a stack you handle yourself, but that would make the code unecessarily complex ...

function Permute ($list)
{
    $global:remove = { 
        param ($element, $list) 

        $newList = @() 
        $list | % { if ($_ -ne $element) { $newList += $_} }  

        return $newList 
    }

    $global:append = {
        param ($head, $tail)

        if ($tail.Count -eq 0)
            { return ,$head }

        $result =  @()

        $tail | %{
            $newList = ,$head
            $_ | %{ $newList += $_ }
            $result += ,$newList
        }

        return $result
    }

    if ($list.Count -eq 0)
        { return @() }

    $list | %{
        $permutations = Permute ($remove.Invoke($_, $list))
        return $append.Invoke($_, $permutations)
    }
}

cls

$list = "x", "y", "z", "t"

$permutations = Permute $list

$permutations | %{
    Write-Host ([string]::Join(", ", $_))
}

There some thinking outside the box. That's a very cool way of doing it, is there a way to condense this into one function? — Bluecakes, Aug 28 '14 at 11:06
See my edit. As I said, this is cheating a bit. But all other alternatives to which I can think of would make the code much more complex. — David Brabant, Aug 28 '14 at 11:52
You sir are a gentleman and scholar, many thanks for the edit. This will give me much to fiddle with to up my knowledge of recursion. — Bluecakes, Aug 28 '14 at 22:46

score 2 · Answer 2 · answered Aug 27 '14 at 22:43

I tried to learn something new and help you out but Im stuck. maybe this will help you get in the right direction but I dont know enough about Powershell recursion to figure this out. I converted the php to powershell and in theory it should work but it doesnt.

$array = @('Alpha', 'Beta', 'Gamma', 'Sigma')


function depth_picker([system.collections.arraylist]$arr,$temp_string, $collect)
{
if($temp_string -ne ""){$collect += $temp_string}
    for($i = 0; $i -lt $arr.count;$i++)
    {
    [system.collections.arraylist]$arrCopy = $arr
    $elem = $arrCopy[$i]
    $arrCopy.removeRange($i,1)
    if($arrCopy.count -gt 0){
    depth_picker -arr $arrCopy -temp_string "$temp_string $elem" -collect $collect}
    else{$collect += "$temp_string $elem"}
    }
}
$collect = @()
depth_picker -arr $array -temp_string "" -collect $collect
$collect

It seems to work and will get you the first set of possibles:

Alpha
Alpha Beta
Alpha Beta Gamma
Alpha Beta Gamma Sigma

But for some reason that I cant figure out when it gets back to the previous functions and does $i++ then checks ($i -lt $arr.count) $arr.count it always 0 so it never goes to the next iteration to continue finding the possibilities.

Hopefully someone else can fix what I cant seem to figure out as I dont know enough about recursion. But it seems that with each level of depth called the previous depth level $arr variable and values is lost.

Yeah i know what you mean, it's doing my head in lol but i'm slowly getting closer every now and then so i got that going for me at least. — Bluecakes, Aug 27 '14 at 23:44

score 0 · Answer 3 · answered Aug 29 '14 at 05:00

Here is my solution with a recursive function. It generates space separated strings but it's quite simple to split each element with $list[$i].split(" "):

function Get-Permutations 
{
    param ($array, $cur, $depth, $list)

    $depth ++
    for ($i = 0; $i -lt $array.Count; $i++)
    {
        $list += $cur+" "+$array[$i]        

        if ($depth -lt $array.Count)
        {
            $list = Get-Permutations $array ($cur+" "+$array[$i]) $depth $list
        }       
    }

    $list
}    

$array = @("first","second","third","fourth")
$list = @()
$list = Get-Permutations $array "" 0 $list

$list

score 0 · Answer 4 · answered Nov 08 '20 at 22:00

The solution posted by Micky Balladelli almost worked for me. Here is a version that does not duplicate values:

Function Get-Permutations 
{
    param ($array_in, $current, $depth, $array_out)
    $depth++
    $array_in = $array_in | select -Unique
    for ($i = 0; $i -lt $array_in.Count; $i++)
    {
        $array_out += ($current+" "+$array_in[$i]).Trim()
        if ($depth -lt $array_in.Count)
        {
            $array_out = Get-Permutations $array_in ($current+" "+$array_in[$i]) $depth $array_out
        }
        else {}
    }
    if(!($array_out -contains ($array_in -Join " "))) {}
    for ($i = 0; $i -lt $array_out.Count; $i++)
    {
        $array_out[$i] = (($array_out[$i].Split(" ")) | select -Unique) -Join " "
    }
    $array_out | select -Unique
}

Get all combinations of an array

4 Answers4

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