Associative Arrays



A compact data structure for storing a collection of keys and values where each key is paired with a value.



An associative array provides a data structure for storing multiple key and value pairs. For example, consider a person's name as a key and that person's birth date as a value. An associative array provides a structure for storing a collection of names and birthdates where each name is mapped to a birth date. Visualize an associative array as a two column table where the first column is a key and the second column is a value.


Associative arrays are similar to a standard array in PowerShell, but rather than referencing the contents of an array by an index number, you reference a data element in an associative array by a key. Using this key, PowerShell returns the mapped value from the associative array.


PowerShell uses the hash table data type for storing the contents of an associative array because this data structure provides a fast lookup mechanism. This is critically important because the primary purpose of an associative array is to provide an efficient lookup mechanism.


In an associative array, you can use heterogeneous data types. For example, you can build an associative array containing an integer, a call to a Cmdlet, and a string, each with a different key.


The following shows the associative array syntax:


$<array name> = @{<key1 = item1>; <key2 = item2>;...}


The way in which you create and initialize an associative array is similar to the way you create and initialize a standard array. However, for an associative array, you must also do the following:


·         Assign a label to each value in the associative array.

·         Append an @ sign to the outside of the array contents.

·         Surround any keys or values that contain spaces with single or double quotes.


For example, to create an associative array named $phone containing phone numbers for Kim Akers, Ken Myers, and Greg Chapman, enter the following one-line command at the PowerShell command-prompt:


$phone = @{'Kim Akers' = '(425) 555-0183'; 'Ken Myers' = '(425) 555-0184'; 'Greg Chapman' = '(425) 555-0185'}


To display the contents of the array, enter the following command:




The output from running this command is as follows:


Key               Value

Ken Myers         (425) 555-0184

Greg Chapman      (425) 555-0185

Kim Akers         (425) 555-0183


There are several ways to selectively display elements. You can use dot notation or array notation. For example, both of the following commands display the telephone number for the Greg Chapman key:


$phone.'Greg Chapman'

$phone['Greg Chapman']


Keys and values require quotes (single or double) only if they contain spaces, otherwise, the quotes are unnecessary. For example, the following one-line command requires no quotes:


$phone = @{Kim_Akers = 4255550183; Ken_Myers = 4255550184; Greg_Chapman = 4255550185}


However, if you intend on storing the value associated with the key as a string literal you should enclose the value in single or double quotes. For example, suppose that you use the following command to create the $phone associative array:


$phone = @{Kim_Akers = 425-555-0183; Ken_Myers = 425-555-0184; Greg_Chapman = 425-555-0185}


The output as a result of entering $phone would be as follows:


Key               Value

Kim_Akers        -313

Greg_Chapman      -315

Ken_Myers        -314


Because single or double quotes are not used when specifying the values, PowerShell interprets the values as integers and the hyphens as subtraction operators (for example, 425-555-0183 = -313). To avoid this problem, you can use the following command:


$phone = @{Kim_Akers = '425-555-0183'; Ken_Myers = '425-555-0184'; Greg_Chapman = '425-555-0185'}


The prior examples demonstrate homogeneous data types contained in an associative array. To verify that the associative array is a hashtable data type, you can use the GetType method, as follows:




To check the data type of an individual element in the associative array, specify the key when calling the $phone associative array, in either of the following ways:





An associative array can contain a mix of data types as the following example demonstrates:


$hashMix = @{Key1 = 1; Key2 = Get-ChildItem ; Key3 = "testing"}


This example demonstrates that Key1 contains an integer, Key2 contains the results of running a Cmdlet, and Key3 contains a string.



For information about arrays, enter the following command at the PowerShell command-prompt:


help about_array


For information about using single and double quotes in strings, enter the following command:


help about_quoting_rules