In the process of learning PowerShell it is customary to hear people say that you shouldn’t re-invent the wheel; if there is a native command for it, you should use that. And I agree. But there is a case to be made for taking the time to properly explore all the different options available to you. For instance when coding for a specific version of PowerShell, or if speed is important. This post will discuss the latter; specifically a comparison of the native command for generating random numbers (Get-Random) and using the .NET class System.Random.

UPDATE! Dave Wyatt commented, correctly, that I was being unfair against Get-Random by using the pipeline. And he is absolutely right! But don’t just take his word for it, check out the updated table – it makes all the difference in the world. This just shows that using the pipeline incorrectly can seriously slow down your script.

This is the script I wrote for the comparisons:

$iterations = 1
$numbers = 10
$method = 'Get-Random'
#$method = 'System.Random'
$random = New-Object -TypeName System.Random

Write-Host "Generating $numbers random number(s) in $iterations iteration(s)."

for ($i = 1; $i -le $iterations; $i++) {
    Measure-Command {
        for ($n = 1; $n -le $numbers; $n++) {
            if ($method -eq 'Get-Random') {
                1..10000 | Get-Random
            }
            elseif ($method -eq 'System.Random') {
                $random.Next(10000)
            }
            else {
                Get-Random -Maximum 10000
            }
        }
    }
}

I ran the code generating 1, 10, 100 and 1000 random numbers for each of the methods (Get-Random and System.Random). I initially wanted to do several iterations and averaging out the results; hence the outer for-loop, but later decided against it, since the numbers where quite clear without needing to take more readings.

Results

Conclusion

As you see, when the numbers go up, the differences between the two methods differ dramatically in favour of using .NET directly. So what can we learn from this? Optimization is important, and taking the extra time to investigate other ways of doing things will usually pay off. If nothing else, you have learned something new. If you just want to generate 1 random number, I personally wouldn’t bother using anything besides the built in Get-Random, but dealing with a great deal of numbers, in this case, using .NET is preferable – at least if you care about speed.

Note that neither of the methods shown here will give you cryptographically secure random numbers. If you need that, check out the RNGCryptoServiceProvider class.