Get-Unique

Module:
Microsoft.PowerShell.Utility

Returns unique items from a sorted list.

Syntax

Get-Unique
   [-InputObject <PSObject>]
   [-AsString]
   [<CommonParameters>]
Get-Unique
   [-InputObject <PSObject>]
   [-OnType]
   [<CommonParameters>]

Description

The Get-Unique cmdlet compares each item in a sorted list to the next item, eliminates duplicates, and returns only one instance of each item. The list must be sorted for the cmdlet to work properly.

Get-Unique is case-sensitive. As a result, strings that differ only in character casing are considered to be unique.

Examples

Example 1: Get unique words in a text file

These commands find the number of unique words in a text file.

$A = $( foreach ($line in Get-Content C:\Test1\File1.txt) {
    $line.tolower().split(" ")
  }) | Sort-Object | Get-Unique
$A.count

The first command gets the content of the File.txt file. It converts each line of text to lowercase letters and then splits each word onto a separate line at the space (" "). Then, it sorts the resulting list alphabetically (the default) and uses the Get-Unique cmdlet to eliminate any duplicate words. The results are stored in the $A variable.

The second command uses the Count property of the collection of strings in $A to determine how many items are in $A.

Example 2: Get unique integers in an array

This command finds the unique members of the set of integers.

1,1,1,1,12,23,4,5,4643,5,3,3,3,3,3,3,3 | Sort-Object | Get-Unique

1
3
4
5
12
23
4643

The first command takes an array of integers typed at the command line, pipes them to the Sort-Object cmdlet to be sorted, and then pipes them to Get-Unique, which eliminates duplicate entries.

Example 3: Get unique object types in a directory

This command uses the Get-ChildItem cmdlet to retrieve the contents of the local directory, which includes files and directories.

Get-ChildItem | Sort-Object {$_.GetType()} | Get-Unique -OnType

The pipeline operator (|) sends the results to the Sort-Object cmdlet. The $_.GetType() statement applies the GetType method to each file or directory. Then, Sort-Object sorts the items by type. Another pipeline operator sends the results to Get-Unique. The OnType parameter directs Get-Unique to return only one object of each type.

Example 4: Get unique processes

This command gets the names of processes running on the computer with duplicates eliminated.

Get-Process | Sort-Object | Select-Object processname | Get-Unique -AsString

The Get-Process command gets all of the processes on the computer. The pipeline operator (|) passes the result to Sort-Object, which, by default, sorts the processes alphabetically by ProcessName. The results are piped to the Select-Object cmdlet, which selects only the values of the ProcessName property of each object. The results are then piped to Get-Unique to eliminate duplicates.

The AsString parameter tells Get-Unique to treat the ProcessName values as strings. Without this parameter, Get-Unique treats the ProcessName values as objects and returns only one instance of the object, that is, the first process name in the list.

Parameters

-AsString

Indicates that this cmdlet uses the data as a string. Without this parameter, data is treated as an object, so when you submit a collection of objects of the same type to Get-Unique, such as a collection of files, it returns just one (the first). You can use this parameter to find the unique values of object properties, such as the file names.

Type:SwitchParameter
Position:Named
Default value:None
Accept pipeline input:False
Accept wildcard characters:False
-InputObject

Specifies input for Get-Unique. Enter a variable that contains the objects or type a command or expression that gets the objects.

This cmdlet treats the input submitted by using InputObject as a collection. it does not enumerate individual items in the collection. Because the collection is a single item, input submitted by using InputObject is always returned unchanged.

Type:PSObject
Position:Named
Default value:None
Accept pipeline input:True
Accept wildcard characters:False
-OnType

Indicates that this cmdlet returns only one object of each type.

Type:SwitchParameter
Position:Named
Default value:None
Accept pipeline input:False
Accept wildcard characters:False

Inputs

PSObject

You can pipe any type of object to Get-Unique.

Outputs

PSObject

The type of object that Get-Unique returns is determined by the input.

Notes

You can also refer to Get-Unique by its built-in alias, gu. For more information, see about_Aliases.

To sort a list, use Sort-Object. You can also use the Unique parameter of Sort-Object to find the unique items in a list.