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!.