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about_Arrays

Updated: May 20, 2009

Applies To: Windows PowerShell 2.0

TOPIC
    about_Arrays

SHORT DESCRIPTION
    Describes a compact data structure for storing data elements.

LONG DESCRIPTION
    An array is a data structure for storing a collection of data elements
    of the same type. Windows PowerShell supports data elements, such as
    string, int (32-bit integer), long (64-bit integer), bool (Boolean), byte,
    and other Microsoft .NET Framework object types. 

  CREATING AND INITIALIZING AN ARRAY
    To create and initialize an array, assign multiple values to a variable.
    The values stored in the array are delimited with a comma and separated
    from the variable name by the assignment operator (=). 

    For example, to create an array named $A that contains the seven
    numeric (int) values of 22, 5, 10, 8, 12, 9, and 80, type:

        $A = 22,5,10,8,12,9,80

    You can also create and initialize an array by using the range 
    operator (..). For example, to create and initialize an array named 
    "$B" that contains the values 5 through 8, type:

        $B = 5..8

    As a result, $B contains four values: 5, 6, 7, and 8.

    When no data type is specified, Windows PowerShell creates each array as
    an object array (type: object[]). To determine the data type of an array, 
    use the GetType() method. For example, to determine the data type of the
    $a array, type:

        $a.gettype()

    To create a strongly typed array, that is, an array that can contain only
    values of a particular type, cast the variable as an array type, such 
    as string[], long[], or int32[]. To cast an array, precede the variable
    name with an array type enclosed in brackets. For example, to create a
    32-bit integer array named $ia containing four integers (1500, 2230, 3350,
    and 4000), type:

        [int32[]]$ia = 1500,2230,3350,4000

    As a result, the $ia array can contain only integers.

    You can create arrays that are cast to any supported type in the
    Microsoft .NET Framework. For example, the objects that Get-Process 
    retrieves to represent processes are of the System.Diagnostics.Process 
    type. To create a strongly typed array of process objects, enter the 
    following command:

        [Diagnostics.Process[]]$zz = Get-Process

    You can populate an array by using the output of a cmdlet, function, or 
    statement. For example, the following statement creates an array that 
    contains the processes that start with the letters "co" and that are 
    running on the current computer:

        $LocalProcesses = get-process co*

    If the statement gets only a single process, the $LocalProcesses variable 
    would not be an array. To ensure the command creates an array, use the 
    array subexpression operator, @, as shown in the following example:

        $LocalProcesses = @(get-process co*)

    Even if the command returns a single process, the $LocalProcesses variable 
    is an array. Even if it has only one member, you can treat it like any 
    other array. For example, you can add other objects to it. For more 
    information, see about_Operators.

 
  READING AN ARRAY
    You can refer to an array by using its variable name, such as $A or $a. 
    Windows PowerShell is not case-sensitive.

    To display all the elements in the array, type the array name. For example:

	$a

    You can refer to the elements in an array by using an index, beginning
    at position 0. Enclose the index number in brackets. For example,
    to display the first element in the $a array, type:

        $a[0]

    To display the third element in the $a array, type:

        $a[2]

    Negative numbers count from the end of the array. For example, "-1" 
    refers to the last element of the array. To display the last three elements
    of the array, type:

        $a[-3..-1]

    However, be cautious when using this notation.

        $a[0..-2]

    This command does not refer to all the elements of the array, except for 
    the last one. It refers to the first, last, and second-to-last elements
    in the array.
   
    You can use the range operator to display a subset of all the values in an 
    array. For example, to display the data elements at index position 1 
    through 3, type:

        $a[1..3]

    You can use the plus operator (+) to combine a range with a list of
    elements in an array. For example, to display the elements at index
    positions 0, 2, and 4 through 6, type:

        $a[0,2+4..6]

    To determine how many items are in an array, combine the range with the
    length property of an array. For example, to display the elements from 
    index position 2 to the end of the array, type:

        $a[2..($a.length-1)]

    The length is set to -1 because the index begins at position 0. Therefore,
    in a three-element array (1,2,3), the index of the third element is 2, 
    which is one less than the length of the array.


    You can also use looping constructs, such as Foreach, For, and While loops,
    to refer to the elements in an array. For example, to use a Foreach loop
    to display the elements in the $a array, type: 

        foreach ($element in $a) {$element}

    The Foreach loop iterates through the array and returns each value in
    the array until reaching the end of the array.

    The For loop is useful when you are incrementing counters while examining
    the elements in an array. For example, to return every other value in an
    array by using a For loop, type:

        for ($i = 0; $i -le ($a.length - 1); $i += 2) {$a[$i]}

    You can use a While loop to display the elements in an array until a 
    defined condition is no longer true. For example, to display the elements
    in the $a array while the array index is less than 4, type:

        $i=0
        while($i -lt 4) {$a[$i]; $i++}

    To learn about the properties and methods of an array, such as the Length 
    property and the SetValue method, use the InputObject parameter of the
    Get-Member cmdlet. When you pipe an array to Get-Member, it displays
    information about the objects in the array. When you use the InputObject
    parameter, it displays information about the array. 

    To find the properties and methods of the $a array, type:

	get-member -inputobject $a


  MANIPULATING AN ARRAY
    You can change the elements in an array, add an element to an array, and
    combine the values from two arrays into a third array.

    To change the value of a particular element in an array, specify the
    array name and the index of the element that you want to change, and then
    use the assignment operator (=) to specify a new value for the element. For
    example, to change the value of the second item in the $a array (index
    position 1) to 10, type:

        $a[1] = 10

    You can also use the SetValue method of an array to change a value. The
    following example changes the second value (index position 1) of the $a
    array to 500:

        $a.SetValue(500,1)

    You can append an element to an existing array by using the += operator.
    This operator adds to an existing value. When the operator is used on an
    element of an array, it increases the value of the element. When the
    operator is used on the array itself, it appends the value. For example,
    to append an element with a value of 200 to the $a array, type:

        $a += 200

    It is not easy to delete elements from an array, but you can create a new
    array that contains only selected elements of an existing array. For
    example, to create the $t array with all the elements in the $a array 
    except for the value at index position 2, type:

        $t = $a[0,1 + 3..($a.length - 1)]

    To combine two arrays into a single array, use the plus operator (+). The
    following example creates two arrays, combines them, and then displays
    the resulting combined array.

        $x = 1,3
        $y = 5,9
        $z = $x + $y

    As a result, the $z array contains 1, 3, 5, and 9.

    To delete an array, use the Remove-Item cmdlet to delete the variable that
    contains the array. The following command specifies the element "a" in the
    Variable: drive. 

        remove-item variable:a

    (For more information about the Variable: drive, see the Variable provider
    Help topic.)


SEE ALSO
    about_Assignment_Operators
    about_Hash_Tables
    about_Operators
    about_For
    about_Foreach
    about_While



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