Update-List

Adds items to and removes items from a property value that contains a collection of objects.

Syntax

Update-List
      [-Add <Object[]>]
      [-Remove <Object[]>]
      [-InputObject <PSObject>]
      [[-Property] <String>]
      [<CommonParameters>]
Update-List
      -Replace <Object[]>
      [-InputObject <PSObject>]
      [[-Property] <String>]
      [<CommonParameters>]

Description

The Update-List cmdlet adds, removes, or replaces items in a property value of an object and returns the updated object. This cmdlet is designed for properties that contain collections of objects.

The Add and Remove parameters add individual items to and remove them from the collection. The Replace parameter replaces the entire collection.

If you do not specify a property in the command, Update-List returns an object that describes the update instead of updating the object. You can submit the update object to cmdlets that change objects, such as Set cmdlets.

This cmdlet works only when the property that is being updated supports the IList interface that Update-List uses. Also, any Set cmdlets that accept an update must support the IList interface.

The core cmdlets that are installed with PowerShell do not support this interface. To determine whether a cmdlet supports Update-List, see the cmdlet Help topic.

This cmdlet was reintroduced in PowerShell 7.

Examples

Example 1: Add items to a property value

In this example we create a class that represents a deck of cards where the cards are stored as a List collection object. The NewDeck() method uses Update-Listto add a complete deck of card values to the cards collection.

class Cards {

    [System.Collections.Generic.List[string]]$cards
    [string]$name

    Cards([string]$_name) {
        $this.name = $_name
        $this.cards = [System.Collections.Generic.List[string]]::new()
    }

    NewDeck() {
        $_suits = "`u{2663}","`u{2666}","`u{2665}","`u{2660}"
        $_values = 'A',2,3,4,5,6,7,8,9,10,'J','Q','K'
        $_deck = foreach ($s in $_suits){ foreach ($v in $_values){ "$v$s"} }
        $this | Update-List -Property cards -Add $_deck | Out-Null
    }

    Show() {
        Write-Host
        Write-Host $this.name ": " $this.cards[0..12]
        if ($this.cards.count -gt 13) {
            Write-Host (' ' * ($this.name.length+3)) $this.cards[13..25]
        }
        if ($this.cards.count -gt 26) {
            Write-Host (' ' * ($this.name.length+3)) $this.cards[26..38]
        }
        if ($this.cards.count -gt 39) {
            Write-Host (' ' * ($this.name.length+3)) $this.cards[39..51]
        }
    }

    Shuffle() { $this.cards = Get-Random -InputObject $this.cards -Count 52 }

    Sort() { $this.cards.Sort() }
}

Note

The Update-List cmdlet outputs the updated object to the pipeline. We pipe the output to Out-Null to suppress the unwanted display.

Example 2: Add and remove items of a collection property

Continuing with the code in Example 1, we will create instances of the Cards class to represent a deck of cards and the cards held by two players. We use the Update-List cmdlet to add cards to the players' hands and to remove cards from the deck.

$player1 = [Cards]::new('Player 1')
$player2 = [Cards]::new('Player 2')

$deck = [Cards]::new('Deck')
$deck.NewDeck()
$deck.Shuffle()
$deck.Show()

# Deal two hands
$player1 | Update-List -Property cards -Add $deck.cards[0,2,4,6,8] | Out-Null
$player2 | Update-List -Property cards -Add $deck.cards[1,3,5,7,9] | Out-Null
$deck | Update-List -Property cards -Remove $player1.cards | Out-Null
$deck | Update-List -Property cards -Remove $player2.cards | Out-Null

$player1.Show()
$player2.Show()
$deck.Show()

Deck :  4♦ 7♥ J♦ 5♣ A♣ 8♦ J♣ Q♥ 6♦ 3♦ 9♦ 6♣ 2♣
        K♥ 4♠ 10♥ 8♠ 10♦ 9♠ 6♠ K♦ 7♣ 3♣ Q♣ A♥ Q♠
        3♥ 5♥ 2♦ 5♠ J♥ J♠ 10♣ 4♥ Q♦ 10♠ 4♣ 2♠ 2♥
        6♥ 7♦ A♠ 5♦ 8♣ 9♥ K♠ 7♠ 3♠ 9♣ A♦ K♣ 8♥

Player 1 :  4♦ J♦ A♣ J♣ 6♦

Player 2 :  7♥ 5♣ 8♦ Q♥ 3♦

Deck :  9♦ 6♣ 2♣ K♥ 4♠ 10♥ 8♠ 10♦ 9♠ 6♠ K♦ 7♣ 3♣
        Q♣ A♥ Q♠ 3♥ 5♥ 2♦ 5♠ J♥ J♠ 10♣ 4♥ Q♦ 10♠
        4♣ 2♠ 2♥ 6♥ 7♦ A♠ 5♦ 8♣ 9♥ K♠ 7♠ 3♠ 9♣
        A♦ K♣ 8♥

The output shows the state of the deck before the cards were dealt to the players. You can see that each player received five cards from the deck. The final output shows the state of the deck after dealing the cards to the players. Update-List was used to select the cards from the deck and add them to the players' collection. Then the players' cards were removed from the deck using Update-List.

Example 3: Add and remove items in a single command

Update-List allows you to use the Add and Remove parameters in a single command. In this example, Player 1 wants to discard the 4♦ and 6♦ and get two new cards.

# Player 1 wants two new cards - remove 2 cards & add 2 cards
$player1 | Update-List -Property cards -Remove $player1.cards[0,4] -Add $deck.cards[0..1] | Out-Null
$player1.Show()

# remove dealt cards from deck
$deck | Update-List -Property cards -Remove $deck.cards[0..1] | Out-Null
$deck.Show()

Player 1 :  J♦ A♣ J♣ 9♦ 6♣

Deck :  2♣ K♥ 4♠ 10♥ 8♠ 10♦ 9♠ 6♠ K♦ 7♣ 3♣ Q♣ A♥
        Q♠ 3♥ 5♥ 2♦ 5♠ J♥ J♠ 10♣ 4♥ Q♦ 10♠ 4♣ 2♠
        2♥ 6♥ 7♦ A♠ 5♦ 8♣ 9♥ K♠ 7♠ 3♠ 9♣ A♦ K♣
        8♥

Parameters

-Add

Specifies the property values to be added to the collection. Enter the values in the order that they should appear in the collection.

Type:Object[]
Position:Named
Default value:None
Accept pipeline input:False
Accept wildcard characters:False
-InputObject

Specifies the objects to be updated. You can also pipe the object to be updated to Update-List.

Type:PSObject
Position:Named
Default value:None
Accept pipeline input:True (ByValue)
Accept wildcard characters:False
-Property

Specifies the property that contains the collection that is being updated. If you omit this parameter, Update-List returns an object that represents the change instead of changing the object.

Type:String
Position:0
Default value:None
Accept pipeline input:False
Accept wildcard characters:False
-Remove

Specifies the property values to be removed from the collection.

Type:Object[]
Position:Named
Default value:None
Accept pipeline input:False
Accept wildcard characters:False
-Replace

Specifies a new collection. This parameter replaces all items in the original collection with the items specified by this parameter.

Type:Object[]
Position:Named
Default value:None
Accept pipeline input:False
Accept wildcard characters:False

Inputs

System.Management.Automation.PSObject

You can pipe the objects to be updated to Update-List.

Outputs

Objects or System.Management.Automation.PSListModifier

Update-List returns the updated object, or it returns an object that represents the update action.