Get-Unique

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

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

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.

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

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.

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.

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.

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.

This example uses case-insensitive comparisons to get unique strings from an array of strings.

"aa", "Aa", "Bb", "bb", "aa" | Sort-Object -CaseSensitive | Get-Unique

aa
Aa
bb
Bb

This example uses case-insensitive comparisons to get unique strings from an array of strings.

"aa", "Aa", "Bb", "bb", "aa" | Sort-Object | Get-Unique -CaseInsensitive

aa
Bb

This cmdlet supports the common parameters: -Debug, -ErrorAction, -ErrorVariable, -InformationAction, -InformationVariable, -OutBuffer, -OutVariable, -PipelineVariable, -ProgressAction, -Verbose, -WarningAction, and -WarningVariable. For more information, see about_CommonParameters.

You can pipe any type of object to this cmdlet.

This cmdlet returns its input objects without duplicates.

PowerShell includes the following aliases for Get-Unique:

• All platforms:
  • 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.