Converting Python script to PowerShell

Question

I'm trying to convert a Python script to PowerShell but I don't have any Python experience and it's getting long for a little piece of code.

def combinliste(seq, k):
    p = []
    i, imax = 0, 2**len(seq)-1
    while i<=imax:
        s = []
        j, jmax = 0, len(seq)-1
        while j<=jmax:
            if (i>>j)&1==1:
                s.append(seq[j])
            j += 1
        if len(s)==k:
            p.append(s)
        i += 1
    return p

I have made something but I really don't know if it's correct. What is += in PowerShell, is it same as Python?

function combinliste {
    Param($seq, $k)
    $p = @()
    $i; $imax = 0, [Math]::Pow(2, $seq.Count) - 1
    while ($i -le $jmax) {
        $s = @()
        $j, $jmax = 0, $seq.Count - 1
        while ($j -le $jmax) {
            if ($i -shr $j -band 1 -eq 1) {
                $s + ($seq ???? #I don't know how to do it here
            }
            $j #humm.. 1
        }
        if ($s.Count -eq $k) {
            $p + $s
        }
        $i #humm.. 1
        return $p
    }
}

I have tried few variations, but I'm lost.

I would recommend that you explain exactly what it is you are trying to accomplish. When every variable name is a single character your code becomes difficult to read and interpret. The more you can explain your code in clear language, along with the output you receive, the output you expect, the difference between the two, and where you're stuck, the more likely you are to get a constructive answer. — anothermh
– anothermh, Commented Dec 30, 2018 at 22:34

Mike Twc · Accepted Answer · 2018-12-31 19:52:23Z

3

function combinliste { param($seq,$k) 

$p = New-Object System.Collections.ArrayList

$i, $imax = 0, ([math]::Pow(2, $seq.Length) - 1)

while ($i -le $imax) {

     $s = New-Object System.Collections.ArrayList
     $j, $jmax = 0, ($seq.Length - 1)
     while ($j -le $jmax) {
         if((($i -shr $j) -band 1) -eq 1) {$s.Add($seq[$j]) | Out-Null}
         $j+=1
         }
     if ($s.Count -eq $k) {$p.Add($s) | Out-Null }
     $i+=1
   }

  return $p
}

$p = combinliste @('green', 'red', 'blue', 'white', 'yellow') 3

$p | foreach {$_ -join " | "}

edited Dec 31, 2018 at 19:52

answered Dec 31, 2018 at 1:19

Mike Twc

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4 Comments

Bacon Bits Over a year ago

$p.Add($s.ToCharArray()) might be closer depending on the use case.

WhyPok Over a year ago

Wow! I believe in Christmas, I wake up and I see under the tree a piece of freshly translated code. Thank you so much!

WhyPok Over a year ago

Just a question, you use ArrayList for $p but not for $s , is there a reason? or an impact on the simplicity of the code ( ex: $p.Add($s) ) ?

Mike Twc Over a year ago

@WhyPok Just updated my answer. I had $s as a string because I assumed that's the input. If you use arrays then arraylist is a better choice then. Actually += operation is pretty inefficient so it's probably not even good for strings if output array is huge.

Ansgar Wiechers · Accepted Answer · 2018-12-30 23:07:01Z

0

The append() method updates an array in-place. The + operator in PowerShell doesn't do that. You need the += assignment operator for it.

$s += $seq[$j]

and

$p += $s

Alternatively you can use ArrayList collections instead of plain arrays:

$s = New-Object 'Collections.ArrayList'

and use their Add() method:

$s.Add($seq[$j]) | Out-Null

The trailing Out-Null is to suppress the index of the appended item that Add() outputs by default.

Side note: you probably need to put the return $p after the outer while loop, and $i; $imax = ... must be $i, $imax = ... for assigning two values to two variables in one statement.

edited Dec 30, 2018 at 23:07

answered Dec 30, 2018 at 22:59

Ansgar Wiechers

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1 Comment

WhyPok Over a year ago

Many thanks to you too ! I saw your answer before going to bed, it makes me sleep well :)

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