PowerShell for Windows Admins

May 25 2019   3:42PM GMT

Stable sort

Richard Siddaway Richard Siddaway Profile: Richard Siddaway

Tags:
Powershell

In Windows PowerShell if you do something like this:

PS> (1..20 | Sort-Object -Property {$_ % 3}) -join ‘ ‘
9 6 12 15 3 18 19 16 13 10 4 1 7 20 17 2 8 11 5 14

The results come back in an unexpected order. This is not a stable sort as the results are sorted by their modulus result but lose the order within each group.

If you want a stable sort – where the results come back from a calculation like this in the order in they were received you need to add the –Stable switch. BUT that was added to PowerShell v6.1 and later

PS> (1..20 | Sort-Object -Property {$_ % 3} -Stable ) -join ‘ ‘
3 6 9 12 15 18 1 4 7 10 13 16 19 2 5 8 11 14 17 20

The results are sorted by modulus result and correctly within each group of modulus results

You could also use the Top or Bottom parameters:

PS> (1..20 | Sort-Object -Property {$_ % 3} -Top 20 ) -join ‘ ‘
3 6 9 12 15 18 1 4 7 10 13 16 19 2 5 8 11 14 17 20
PS> (1..20 | Sort-Object -Property {$_ % 3} -Bottom 20 ) -join ‘ ‘
3 6 9 12 15 18 1 4 7 10 13 16 19 2 5 8 11 14 17 20

If you alter the values presented to Top and Bottom you’ll get a subset of the results

PS> (1..20 | Sort-Object -Property {$_ % 3} -Top 10 ) -join ‘ ‘
3 6 9 12 15 18 1 4 7 10
PS> (1..20 | Sort-Object -Property {$_ % 3} -Bottom 10 ) -join ‘ ‘
13 16 19 2 5 8 11 14 17 20

Sort-Object in PowerShell Core has an interesting set of additions compared to Windows PowerShell.

 Comment on this Post

 
There was an error processing your information. Please try again later.
Thanks. We'll let you know when a new response is added.
Send me notifications when other members comment.

Forgot Password

No problem! Submit your e-mail address below. We'll send you an e-mail containing your password.

Your password has been sent to:

Share this item with your network: