Using System.Random in PowerShell to Retrieve a Random List from an Array - powershell

Question

I need a list of generated six-digit numbers
First I generated a list of numbers.
$Numbers += 0..999999 | ForEach-Object {
if ( ($_ -as [string]).Length -eq 1 ) {
"00000$_"
}elseif ( ($_ -as [string]).Length -eq 2 ) {
"0000$_"
}elseif ( ($_ -as [string]).Length -eq 3 ) {
"000$_"
}elseif ( ($_ -as [string]).Length -eq 4 ) {
"00$_"
}elseif ( ($_ -as [string]).Length -eq 5 ) {
"0$_"
}else{$_ -as [string]}
}
Next, I shuffle the list.
$RandomNumbers = $Numbers | Sort-Object { Get-Random }
And that's exactly what takes too long for me.
Is there a way to have the numbers sorted faster?
I thought about "System.Random", but I couldn't get it to work.

Answer 1

You can use Get-Random not only to generate random numbers but also to efficiently shuffle a collection:
$RandomNumbers = Get-Random -InputObject $Numbers -Count $Numbers.Count
This takes less than a second on my machine for one million numbers, whereas your original code took 27 seconds.
As expected, the $RandomNumbers array only contains unique numbers, which I have verified using ($RandomNumbers | Sort-Object -unique).Count which outputs 1000000.
If you have PowerShell 7+ available, you can slightly simplify the code by replacing the the -Count parameter with the -Shuffle parameter:
$RandomNumbers = Get-Random -InputObject $Numbers -Shuffle

Answer 2

The problem here is not that Get-Random is particularly slow, it's that you're generating way more data than necessary. As jdweng comments:
Only generate the minimum number of random numbers that you need.
If you only need 1000 numbers between 0 and 999999, call Get-Random only 1000 times:
$RandomNumbers = 1..1000 |ForEach-Object {
'{0:d6}' -f (Get-Random -Min 0 -Max 1000000)
}
If the numbers have to be distinct, you can use a HashSet<int> or a hashtable to keep track of unique values until you reach the desired amount:
$NumberCount = 1000
$newNumbers = #{}
while($newNumbers.psbase.Count -lt $NumberCount){
$newNumbers[(Get-Random -Min 0 -Max 1000000)] = $true
}
$RandomNumbers = $newNumbers.psbase.Keys |ForEach-Object ToString d6