about arrays.help

8/12/2019 About Arrays.help

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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 rangeoperator (..). 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, suchas 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.Processtype. To create a strongly typed array of process objects, enter thefollowing command:

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

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


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$LocalProcesses = get-process co*

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

$LocalProcesses = @(get-process co*)

Even if the command returns a single process, the $LocalProcesses variableis an array. Even if it has only one member, you can treat it like anyother array. For example, you can add other objects to it. For moreinformation, 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 forthe 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 anarray. For example, to display the data elements at index position 1through 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


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length property of an array. For example, to display the elements fromindex 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 adefined 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 Lengthproperty 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)


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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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