Prof. Powershell

Math Matters

Hate math? Hate it no longer when you invoke the .NET Math class for this week's data formatting tip.

• By Jeffery Hicks
• 09/18/2012

I'm sure many of you have either seen code like this if not run it yourself:

PS C:\> Get-WmiObject win32_logicaldisk -filter "drivetype=3" | Select DeviceId,Size,Freespace

DeviceId                   Size        Freespace
--------                   ----        ---------
C:                 201504845824      134099279872
D:                  32499560448        5596352512
E:                    209711104         135725056

You've probably also tried to reformat the number to something more meaningful, such as megabytes:

PS C:\> Get-WmiObject win32_logicaldisk -filter "drivetype=3" | Select DeviceID,@{Name="SizeMB";Expression={$_.Size/1MB}},@{Name="FreeMB";Expression={$_.Freespace/1MB}}

DeviceID                 SizeMB           FreeMB
--------                 ------           ------
C:              192169.99609375   127881.6796875
D:               30993.99609375    5337.09765625
E:                 199.99609375         129.4375

Of course very few people like all those decimal points. So you might try shortening them with this:

PS C:\> Get-WmiObject win32_logicaldisk -filter "drivetype=3" | Select DeviceID,@{Name="SizeMB";Expression={"{0:N2}" -f ($_.Size/1MB)}},
@{Name="FreeMB";Expression={"{0:N2}" -f ($_.Freespace/1MB)}}

DeviceID       SizeMB          FreeMB
--------       ------          ------
C:             192,170.00      127,887.63
D:             30,994.00       5,337.10
E:             200.00          129.44

This certainly looks better and if all you want is a simple formatted report, this is fine. But what you see is not what you get. Look at this:

PS C:\> Get-WmiObject win32_logicaldisk -filter "drivetype=3" |
Select DeviceID,@{Name="SizeMB";Expression={"{0:N2}" -f ($_.Size/1MB)}},
@{Name="FreeMB";Expression={"{0:N2}" -f ($_.Freespace/1MB)}} | Sort FreeMB -Descending

DeviceID       SizeMB          FreeMB
--------       ------          ------
D:             30,994.00       5,337.10
E:             200.00          129.44
C:             192,170.00      127,880.50

It's clearly not sorting in the expected order. That's because when you use the -f operator, it creates a string value. If you had a numeric value property from many machines you won't get the results you expect.

One solution is to convert this string back into a number:

PS C:\> Get-WmiObject win32_logicaldisk -filter "drivetype=3" |
Select DeviceID,@{Name="SizeMB";Expression={("{0:N2}" -f ($_.Size/1MB)) -as [double]}},@{Name="FreeMB";Expression={("{0:N2}" -f ($_.Freespace/1MB)) -as [double]}} | Sort FreeMB -Descending

DeviceID         SizeMB         FreeMB
--------         ------         ------
C:               192170      127881.47
D:                30994         5337.1
E:                  200         129.44

That's more like it, but it sure seems like a lot of work. Here's a better way using the .NET Math class.

There are no math cmdlets, but you can access the math library by using [Math]. You can't create a math object, but once you know the method, you can simply invoke it. Here's a one-liner to help show you the methods:

([math]).GetMethods() | sort name | Select Name -unique

Once you know the method, then you can run commands like this:

PS C:\> [math]::Sqrt(25)
5

PS C:\> [math]::Pow(2,10)
1024

PS C:\> [math]::Round(123.45678,2)
123.46

It's that last method that we're interested in. The method needs a number and number of decimal places. The best part is that it writes a numeric object, technically a double in this example, to the pipeline. Thus, we can modify our WMI query accordingly:

PS C:\> Get-WmiObject win32_logicaldisk -filter "drivetype=3" |
Select DeviceID,@{Name="SizeMB";Expression={[math]::Round($_.Size/1MB,2)}},
@{Name="FreeMB";Expression={[math]::Round($_.Freespace/1MB,2)}} | Sort FreeMB -Descending

DeviceID        SizeMB         FreeMB
--------        ------         ------
C:              192170      127884.68
D:               30994         5337.1
E:                 200         129.44

I haven't found a good and easy way to force PowerShell to include the trailing 0, but I can live with this. If you don't want any decimal points, simply eliminate the second parameter value in the Round() method. But now I have a way to get numeric data in the format I want without sacrificing anything.