PowerShell Sort Array

eddik

　　Note: This is part two of a multiple blog series about working with arrays and hash tables for data storage. In yesterday’s Hey, Scripting Guy! Blog,Learn Simple Ways to Handle Windows PowerShell Arrays, I discussed creating arrays, indexing into arrays, and two techniques for walking through an array.
Working with specific array elements
　　One of the interesting things about arrays in Windows PowerShell is they are able to hold different data types. For example, I can store numbers and strings in the same array as shown here.
PS C:\> $a = 1,2,3,"four"
PS C:\> $a
1
2
3
Four
Changing element values
　　If I need to change an element in array, I can index into the array by using the square bracket and the index number. To find the upper boundary, I use theGetUpperBoundmethod, and when I have that value, I can easily find the element I need to modify. This technique is shown here.
PS C:\> $a.GetUpperBound(0)
3
PS C:\> $a[3] = 4
PS C:\> $a
1
2
3
4
Adding a new element to an existing array
　　If I want to add an element to an existing array, it might make sense to choose the next index number, and attempt to assign a value in the same way that I change an existing value. When I do this, however, Windows PowerShell generates an out of range errormessage. This command and error message are shown here.
PS C:\> $a[4] = 12
Array assignment failed because index '4' was out of range.
At line:1 char:4
+ $a[ <<<< 4] = 12
+ CategoryInfo : InvalidOperation: (4:Int32) [], RuntimeException
+ FullyQualifiedErrorId : IndexOutOfRange
　　The way to add a new element to an existing array is to use the += operator as shown here.
$a += 12
　　The commands to create an array, get the upper boundary of an array, change an element in an array, and add a new element to an array are shown here with their associated output.

Searching for a specific value in an array
　　One question that comes up from time-to-time is, “How do I know whether a value is contained in an array?” The answer is, once again, rather easy, “Use theContainsoperator”. The following two commands use the previously created$a array. In the first command, the number 12 is present, and the valueTruereturns. In the second example, the array does not contain the number 14; and therefore, the returned value isFalse.
PS C:\> $a -contains 12
True
PS C:\> $a -contains 14
False
PS C:\>
Sorting an array
　　Now suppose I need to sort my array. There are actually two ways to do this. The first way to do this is to use theSort-Object cmdlet (Sort is an alias for the Sort-Object cmdlet). The second way to sort an array is to use the staticSortmethod from the System.Array .NET Framework class.
Use Sort and the pipeline
　　The first technique I will discuss is also the easiest to use. It is the pipeline method. All that this technique requires is to pipe the array to the cmdlet. This technique is shown here.
PS C:\> [int[]]$a = 1,5,7,2,12,4
PS C:\> $a | Sort-Object
1
2
4
5
7
12
　　The thing to keep in mind is that this does not change the array, it merely changes the display output. If I want to modify the actual array, I need to write the results back to the original array. This technique is shown here.
PS C:\> $a = $a | sort
PS C:\> $a
1
2
4
5
7
12
　　The commands to create an array of integers, sort the results with the Sort-Object cmdlet, and write the results back to the array are shown in the following image.

Use Get-Random to create a random array
　　One of my favorite tricks is to create an array of numbers by using the Get-Random cmdlet. To do this, I use Countto specify the number of values to select, and I use a range operator to create an array of numbers from which to choose. I then write the random values to a variable. This techniqueis shown here.
$rnd = Get-Random -Count 10 -InputObject (1..100000)
Use the static Sortmethod
　　To sort the random numbers, I use the Sortstatic method from theSystem.Array .NET Framework class. Because Sortis a static method, I need to use a double colon separator between the class name (in square brackets) and the method name. I supply the array of random numbers as an input value. This command is shown here.
[array]::sort($rnd)
　　What is really interesting is that the Sortstatic method, automatically writes the sorted values back to the array that is contained in the$rnd variable. The commands to create a random array of numbers, display those values, sort the array, and display the sorted list are shown in the following image.

Measuring the difference in performance
　　“So, what is the difference between the two ways to sort arrays,” you may ask. The difference is that the pipeline way of sorting is probably more intuitive to Windows PowerShell users. The other difference is that the staticSortmethod from the System.Array class is way faster. To check this, I like to use theMeasure-Command cmdlet. To ensure I have a large enough data set that will take a decent amount of time to sort, I create two random arrays by using the commands that are shown here.
$arrayA = Get-Random -Count 1000000 -InputObject (1..1000000)
$arrayB = Get-Random -Count 1000000 -InputObject (1..1000000)
　　Next, I use the Measure-Command cmdlet to measure the two ways of sorting arrays. The two commands are shown here.
Measure-Command -Expression { $arrayA = $arrayA | Sort-Object }
Measure-Command -Expression { [array]::Sort($arrayB) }
　　On my system (which is a fast computer), the first command takes a little over 40 seconds, whereas the second command takes a little more than 8 seconds. Therefore, the second command appears to be five times faster than the first command that uses the pipeline.
　　The commands that create the two random arrays use Measure-Command to check the speed of the two commands, and they display the first two numbers in each of the newly sorted arrays, as shown in the following image.

　　Sorting arrays that contain multiple types
　　There is one more caveat when it comes to using the two sort methods. Because an array in Windows PowerShell can contain different types, theSort-Object method may be the preferred way of sorting objects. This is because in using the default comparer, theSortstatic method fails when the array contains different types.
　　In the following example, I create an array that contains both integers and strings. I then pipe the array to theSort-Object cmdlet (using Sort as the alias). Next, I attempt to use the staticSort method from the System.Array class, and that generates an error message.
PS C:\> $array = 1,2,9,8,3,"four","tree","Cat","bat"
PS C:\> $array | sort
1
2
3
8
9
bat
Cat
four
tree
PS C:\> [array]::sort($array)
Exception calling "Sort" with "1" argument(s): "Failed to compare two elements in the array."
At line:1 char:14
+ [array]::sort <<<< ($array)
+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : DotNetMethodException

PS C:\>
　　Because an array can contain other objects (besides strings and integers), I decide to perform one additional test, and I therefore store an instance of theSystem.Diagnostics.Process .NET Framework class in the last element. This command is shown here.
PS C:\> $array = 1,2,9,8,3,"four","tree","Cat","bat",(get-process winword)
PS C:\> $array
1
2
9
8
3
four
tree
Cat
bat

Handles NPM(K) PM(K) WS(K) VM(M) CPU(s) Id ProcessName
------- ------ ----- ----- ----- ------ -- -----------
463 62 41772 89736 369 39.17 4460 WINWORD
　　Next, I decide to sort the array. Once again, the Sort-Object cmdlet comes through with no problems. This output is shown here.
PS C:\> $array | sort
1
2
3
8
9
bat
Cat
four

Handles NPM(K) PM(K) WS(K) VM(M) CPU(s) Id ProcessName
------- ------ ----- ----- ----- ------ -- -----------
463 62 41772 89736 369 39.17 4460 WINWORD
tree


PS C:\>
　　PT, that is all there is to modifying values in an array, adding to an array, checking to see if an array contains a specific value, and sorting the array. Array Week will continue tomorrow when I will store different types of objects in an array (includingother arrays). It will be fun and educational. See ya!
　　I invite you to follow me on Twitter and Facebook. If you have any questions, send email to me atscripter@microsoft.com, or post your questions on theOfficial Scripting Guys Forum. See you tomorrow. Until then, peace.