Select and then Sort

When you use both select-object and sort-object in a pipeline, what's the proper order? Let's check how fast they execute.
Each speed test is built from two similar commands with a different sort/select piping order and each test is executed 10 times. The total execution time is measured in Milliseconds.

- Updated: 06/11/2008 (see comment below by Lee Holmes) -

Test #1

PS > (measure-Command { 1..10 | foreach { gsv | sort name | select name,status }}).TotalMilliseconds

444.5451


PS > (measure-Command { 1..10 | foreach { gsv | select name,status | sort name}}).TotalMilliseconds

384.7565

Result: Second command is 15% faster.

Test #2  

# this command is the third example of select-object command from the help files.

PS > (measure-command { 1..10 | foreach { gps | sort ws | select -last 5 }}).TotalMilliseconds

346.0652


PS > (measure-command { 1..10 | foreach { gps | select -last 5 | sort WS }}).TotalMilliseconds

100.4444
    
Result: Second command is 3.44 times faster.

# this command is the sixth example of sort-object command from the CTP help files. I changed the extension to ps1.

PS > (measure-Command { 1..10 | foreach { dir *.ps1 | sort @{Expression={$_.LastWriteTime-$_.CreationTime}; Ascending=$
false} | select LastWriteTime, CreationTime}}).TotalMilliseconds

640.9769

PS > (measure-Command { 1..10 | foreach { dir *.ps1 | select LastWriteTime, CreationTime | sort @{Expression={$_.LastWr
iteTime-$_.CreationTime}; Ascending=$false}}}).TotalMilliseconds

592.3512

 Result: Second command is 8.2% faster

Test #3  

PS > (measure-Command { 1..10 | foreach { dir | sort -unique | select name}}).TotalMilliseconds

6405.653


PS > (measure-Command { 1..10 | foreach { dir | select name | sort -unique}}).TotalMilliseconds

750.8251

Result: Second command is 753% faster!

The reason why 'select then sort' is faster to execute is because there are much less properties for sort-object to work on. When you select certain properties from a collection, select-object creates a new object with just the specified properties of the incoming object thus resulting in a smaller object to process.

One thing is for sure: In most cases, select objects before sorting them, and ALWAYS make sure they produce the SAME output!.

Generating Random Dates

One of the new cmdlets in PowerShell CTP2 is Get-Random. Get-Random gets a random number or selects objects randomly from a collection. 

I wanted to generate random DateTime objects with it but there is no built-in capability for that, yet it doesn't mean you can't use Get-Random it to generate random dates :)

At its base, a DateTime object is measured in 100-nanosecond units called Ticks. So I tried to use Get-Date to initialize a DateTime using Ticks. Again, Get-Date doesn't have any parameter for that so I checked the underlying object, System.DateTime.

One of the System.DateTime constructors allows you to initialize a new instance of the DateTime structure to a specified number of ticks. The maximum value for ticks is determined by:

PS > [datetime]::maxValue.ticks 
3155378975999999999

Now, Can I use Get-Random to generate a number in the range of 0-3155378975999999999 (exclusive)? 
The help for Get-Random says: Without parameters or input, "Get-Random" returns a randomly selected 32-bit unsigned integer between 0 and Int32.MaxValue (0x7FFFFFFF, 2,147,483,647), so it shouldn't be a problem with the ticks input to generate a higher value then the max value of Int32.MaxValue:
 

PS > Get-Random ([datetime]::maxValue.ticks) 
1.34540044929813E+18 

PS > Get-Random ([datetime]::maxValue.ticks) 
8.71609536968019E+17 

Yes I can! So I tried to generate a new DateTime using that method:

PS > [datetime]::maxValue.ticks 
3155378975999999999

PS > new-object dateTime (Get-Random ([datetime]::maxValue.ticks)) 
Friday, March 09, 3951 11:00:06 PM

PS > new-object dateTime (Get-Random ([datetime]::maxValue.ticks)) 
Wednesday, October 07, 2476 1:36:05 AM 

Cool. But this can give a date between the Year 0 and 9999:

PS > new-object datetime ([datetime]::maxValue.ticks)
Friday, December 31, 9999 11:59:59 PM

If you want to have random DateTime between a specific period of time then you can use the Get-Random -min and -max parameters:

PS > $dateMin = get-date -year 1980 -month 1 -day 1 
PS > $dateMax = get-date -year 2007 -month 1 -day 1

PS > new-object datetime (Get-Random -min $dateMin.ticks -max $dateMax.ticks) 
Thursday, November 14, 2002 9:45:23 AM 

PS > new-object datetime (Get-Random -min $dateMin.ticks -max $dateMax.ticks)
Friday, December 07, 2001 6:17:54 PM 

PS > new-object datetime (Get-Random -min $dateMin.ticks -max $dateMax.ticks) 
Monday, April 01, 2002 4:50:52 PM

I didn't find any use for random dates yet, but it is good to know you can create them.

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I need to try it in WPF forms! This week, the PowerShell blog sphere is full with WPF walk through's introduced by Joel, MoW and James Brundage from the PowerShell team.

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PowerScripting Podcast - Episode 26

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And for a limited time, Quest, the sponsor of the PowerScripting Podcast is offering Powerscripting Podcast listeners a free copy of Jeffery Hicks [MVP] upcoming book, 'Managing Active Directory with Windows PowerShell: TFM' from Sapien Press. Get the full details at the PowerScripting Podcast website.

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