about_Hash_Tables
Short description
Describes how to create, use, and sort hashtables in PowerShell.
Long description
A hashtable, also known as a dictionary or associative array, is a compact data structure that stores one or more key-value pairs. For example, a hash table might contain a series of IP addresses and computer names, where the IP addresses are the keys and the computer names are the values, or vice versa.
In PowerShell, each hashtable is a [System.Collections.Hashtable] object. You
can use the properties and methods of Hashtable objects in PowerShell.
Beginning in PowerShell 3.0, you can use the [ordered] type accelerator to
create an [System.Collections.Specialized.OrderedDictionary] object in
PowerShell.
Ordered dictionaries differ from hashtables in that the keys always appear in the order in which you list them. The order of keys in a hashtable isn't deterministic.
The keys and value in hashtables are also .NET objects. They're most often strings or integers, but they can have any object type. You can also create nested hashtables, in which the value of a key is another hashtable.
Hashtables are frequently used because they're efficient for finding and
retrieving data. You can use hashtables to store lists and to create calculated
properties in PowerShell. And, the ConvertFrom-StringData cmdlet converts
structured string data to a hashtable.
Syntax
The syntax of a hashtable is as follows:
@{ <name> = <value>; [<name> = <value> ] ...}
The syntax of an ordered dictionary is as follows:
[ordered]@{ <name> = <value>; [<name> = <value> ] ...}
The [ordered] type accelerator was introduced in PowerShell 3.0.
To create a hashtable, follow these guidelines:
- Begin the hashtable with an at sign (
@). - Enclose the hashtable in braces (
{}). - Enter one or more key-value pairs for the content of the hashtable.
- Use an equal sign (
=) to separate each key from its value. - Use a semicolon (
;) or a line break to separate the key-value pairs. - Keys that contain spaces must be enclosed in quotation marks. Values must be valid PowerShell expressions. Strings must appear in quotation marks, even if they don't include spaces.
- To manage the hashtable, save it in a variable.
- When assigning an ordered hashtable to a variable, place the
[ordered]type before the@symbol. If you place it before the variable name, the command fails.
You can use ordered dictionaries in the same way that you use hashtables. Either type can be used as the value of parameters that take a hashtable or dictionary (iDictionary) type objects.
Creating hashtables and ordered dictionaries
Consider the following hashtable and ordered dictionary examples:
$hash = @{
1 = 'one'
2 = 'two'
'three' = 3
}
$hash
Name Value
---- -----
three 3
2 two
1 one
As you can see, the key-value pairs in a hashtable aren't presented in the order that they were defined.
The easiest way to create an ordered dictionary is to use the [ordered]
attribute. Place the attribute immediately before the @ symbol.
$dictionary = [ordered]@{
1 = 'one'
2 = 'two'
'three' = 3
}
$dictionary
Name Value
---- -----
1 one
2 two
three 3
Unlike hashtables, ordered dictionaries maintain the order of the key-value.
Converting hashtables and ordered dictionaries
You can't use the [ordered] type accelerator to convert or cast a hashtable.
If you place the ordered attribute before the variable name, the command fails
with the following error message.
[ordered]$orderedhash = @{}
ParserError:
Line |
1 | [ordered]$orderedhash = @{}
| ~~~~~~~~~~~~~~
| The ordered attribute can be specified only on a hash literal node.
To correct the expression, move the [ordered] attribute.
$orderedhash = [ordered]@{}
You can cast an ordered dictionary to a hashtable, but you can't guarantee the order of the members.
[hashtable]$newhash = [ordered]@{
Number = 1
Shape = "Square"
Color = "Blue"
}
$newhash
Name Value
---- -----
Color Blue
Shape Square
Number 1
Hashtable and dictionary properties
Hashtables and ordered dictionaries share several properties. Consider the
$hash and $dictionary variables defined in the previous examples.
$hash | Get-Member -MemberType Properties, ParameterizedProperty
TypeName: System.Collections.Hashtable
Name MemberType Definition
---- ---------- ----------
Item ParameterizedProperty System.Object Item(System.Object key) {get;set;}
Count Property int Count {get;}
IsFixedSize Property bool IsFixedSize {get;}
IsReadOnly Property bool IsReadOnly {get;}
IsSynchronized Property bool IsSynchronized {get;}
Keys Property System.Collections.ICollection Keys {get;}
SyncRoot Property System.Object SyncRoot {get;}
Values Property System.Collections.ICollection Values {get;}
$dictionary | Get-Member -MemberType Properties, ParameterizedProperty
TypeName: System.Collections.Specialized.OrderedDictionary
Name MemberType Definition
---- ---------- ----------
Item ParameterizedProperty System.Object Item(int index) {get;set;},
System.Object Item(System.Object key) {get;set;}
Count Property int Count {get;}
IsFixedSize Property bool IsFixedSize {get;}
IsReadOnly Property bool IsReadOnly {get;}
IsSynchronized Property bool IsSynchronized {get;}
Keys Property System.Collections.ICollection Keys {get;}
SyncRoot Property System.Object SyncRoot {get;}
Values Property System.Collections.ICollection Values {get;}
The most-used properties are Count, Keys, Values, and Item.
The Count property that indicates the number of key-value pairs in the object.
The Keys property is a collection of the key names in the hashtable or dictionary.
PS> $hash.Keys three 2 1 PS> $dictionary.Keys 1 2 threeThe Values property is a collection of the values in the hashtable or dictionary.
PS> $hash.Values 3 two one PS> $dictionary.Values one two 3The Item property is a parameterized property that returns the value of the item that you specify. Hashtables use the key as the parameter to the parameterized property, while dictionaries use the index by default. This difference affects how you access the values for each type.
Accessing values
There are two common ways to access the values in a hashtable or dictionary: member notation or array index notation.
Member notation - Values can be accessed by using the key name as a member property of the object. For example:
PS> $hash.1 one PS> $dictionary.2 twoArray index notation - Values can be accessed by using index notation. PowerShell converts that notation into a call to Item parameterized property of the object.
When you use index notation with hashtables, the value inside of the brackets is the key name. If the key is a string value, enclose the key name in quotes. For example:
PS> $hash['three'] 3 PS> $hash[2] 2In this example, the key value
2isn't an index into the collection of values. It's the value of the key in the key-value pair. You can prove this by indexing into the collection of values.PS> ([array]$hash.Values)[2] oneWhen you use index notation with dictionaries, the value inside of the brackets is interpreted based on its type. If the value is an integer, it's treated as an index into the collection of values. If the value isn't an integer, it's treated as the key name. For example:
PS> $dictionary[1] two PS> ([array]$dictionary.Values)[1] two PS> $dictionary[[object]1] one PS> $dictionary['three'] 3In this example, the array value
[1]is an index into the collection of values using theItem(int index)parameterized property overload. The array value[[object]1]isn't an index but a key value using theItem(System.Object key)overload.Note
This behavior can be confusing when the key value is an integer. When possible, you should avoid using integer key values in dictionaries.
Handling property name collisions
If the key name collides with one of the property names of the HashTable
type, you can use the psbase intrinsic member
to access those properties. For example, if the key name is keys and you want
to return the collection of the HashTable keys, use this syntax:
$hashtable.psbase.Keys
This requirement applies for other types that implement the System.Collections.IDictionary interface, like OrderedDictionary.
Iterating over keys and values
You can iterate over the keys in a hashtable to process the values in several
ways. Each of the examples in this section has identical output. They iterate
over the $hash variable defined here:
$hash = [ordered]@{ Number = 1; Shape = "Square"; Color = "Blue"}
Note
In these examples, $hash is defined as an ordered dictionary to ensure the
output is always in the same order. These examples work the same for standard
hashtables, but the order of the output isn't predictable.
Each example returns a message for every key and its value:
The value of 'Number' is: 1
The value of 'Shape' is: Square
The value of 'Color' is: Blue
This example uses a foreach block to iterate over the keys.
foreach ($Key in $hash.Keys) {
"The value of '$Key' is: $($hash[$Key])"
}
This example uses ForEach-Object to iterate over the keys.
$hash.Keys | ForEach-Object {
"The value of '$_' is: $($hash[$_])"
}
This example uses the GetEnumerator() method to send each key-value pair
through the pipeline to ForEach-Object.
$hash.GetEnumerator() | ForEach-Object {
"The value of '$($_.Key)' is: $($_.Value)"
}
This example uses the GetEnumerator() and ForEach() methods to iterate over
each key-value pair.
$hash.GetEnumerator().ForEach({"The value of '$($_.Key)' is: $($_.Value)"})
Adding and Removing Keys and Values
Typically, when you create a hashtable you include the key-value pairs in the definition. However, you can add and remove key-value pairs from a hashtable at any time. The following example creates an empty hashtable.
$hash = @{}
You can add key-value pairs using array notation. For example, the following
example adds a Time key with a value of Now to the hashtable.
$hash["Time"] = "Now"
You can also add keys and values to a hashtable using the Add() method of the
System.Collections.Hashtable object. The Add() method has the following
syntax:
Add(Key, Value)
For example, to add a Time key with a value of Now to the hashtable, use
the following statement format.
$hash.Add("Time", "Now")
And, you can add keys and values to a hashtable using the addition operator
(+) to add a hashtable to an existing hashtable. For example, the following
statement adds a Time key with a value of Now to the hashtable in the
$hash variable.
$hash = $hash + @{Time="Now"}
You can also add values that are stored in variables.
$t = "Today"
$now = (Get-Date)
$hash.Add($t, $now)
You can't use a subtraction operator to remove a key-value pair from a hash
table, but you can use the Remove() method of the hashtable object. The
Remove method has the following syntax:
$object.Remove(<key>)
The following example removes the Time key-value pair from $hash.
$hash.Remove("Time")
Object Types in HashTables
The keys and values in a hashtable can have any .NET object type, and a single hashtable can have keys and values of multiple types.
The following statement creates a hashtable of process name strings and process
object values and saves it in the $p variable.
$p = @{
"PowerShell" = (Get-Process pwsh)
"Notepad" = (Get-Process notepad)
}
You can display the hashtable in $p and use the key-name properties to
display the values.
PS> $p
Name Value
---- -----
PowerShell System.Diagnostics.Process (pwsh)
Notepad System.Diagnostics.Process (notepad)
PS> $p.PowerShell
Handles NPM(K) PM(K) WS(K) VM(M) CPU(s) Id ProcessName
------- ------ ----- ----- ----- ------ -- -----------
441 24 54196 54012 571 5.10 1788 PowerShell
PS> $p.keys | ForEach-Object {$p.$_.Handles}
774
824
The keys in a hashtable can be any .NET type. The following statement adds a
key-value pair to the hashtable in the $p variable. The key is a Service
object that represents the WinRM service, and the value is the current status
of the service.
$p = $p + @{
(Get-Service WinRM) = ((Get-Service WinRM).Status)
}
You can display and access the new key-value pair using the same methods that you use for other pairs in the hashtable.
PS> $p
Name Value
---- -----
PowerShell System.Diagnostics.Process (pwsh)
WinRM Running
Notepad System.Diagnostics.Process (Notepad)
PS> $p.keys
PowerShell
Status Name DisplayName
------ ---- -----------
Running WinRM Windows Remote Management (WS-Managem…
Notepad
The keys and values in a hashtable can also be Hashtable objects. The following
statement adds key-value pair to the hashtable in the $p variable in which
the key is a string, Hash2, and the value is a hashtable with three key-value
pairs.
$p = $p + @{
"Hash2"= @{a=1; b=2; c=3}
}
You can display and access the new values using the same methods.
PS> $p
Name Value
---- -----
WinRM Running
Hash2 {a, b, c}
PowerShell System.Diagnostics.Process (pwsh)
Notepad System.Diagnostics.Process (Notepad)
PS> $p.Hash2
Name Value
---- -----
a 1
b 2
c 3
PS> $p.Hash2.b
2
Sorting Keys and Values
The items in a hashtable are intrinsically unordered. The key-value pairs might appear in a different order each time that you display them.
Although you can't sort a hashtable, you can use the GetEnumerator() method
of hashtables to enumerate the keys and values, and then use the Sort-Object
cmdlet to sort the enumerated values for display.
For example, the following commands enumerate the keys and values in the hash
table in the $p variable and then sort the keys in alphabetical order.
PS> $p.GetEnumerator() | Sort-Object -Property key
Name Value
---- -----
Hash2 {a, b, c}
Notepad System.Diagnostics.Process (Notepad)
PowerShell System.Diagnostics.Process (pwsh)
WinRM Running
The following command uses the same procedure to sort the hash values in descending order.
PS> $p.GetEnumerator() | Sort-Object -Property Value -Descending
Name Value
---- -----
PowerShell System.Diagnostics.Process (pwsh)
Notepad System.Diagnostics.Process (Notepad)
Hash2 {a, b, c}
WinRM Running
Creating Objects from hashtables
Beginning in PowerShell 3.0, you can create an object from a hashtable of properties and property values.
The syntax is as follows:
[<class-name>]@{
<property-name>=<property-value>
<property-name>=<property-value>
}
This method works only for classes that have a constructor that has no parameters. The object properties must be public and settable.
For more information, see about_Object_Creation.
ConvertFrom-StringData
The ConvertFrom-StringData cmdlet converts a string or a here-string of
key-value pairs into a hashtable. You can use the ConvertFrom-StringData
cmdlet safely in the Data section of a script, and you can use it with the
Import-LocalizedData cmdlet to display user messages in the user-interface
(UI) culture of the current user.
Here-strings are especially useful when the values in the hashtable include quotation marks. For more information about here-strings, see about_Quoting_Rules.
The following example shows how to create a here-string of the user messages in
the previous example and how to use ConvertFrom-StringData to convert them
from a string into a hashtable.
The following command creates a here-string of the key-value pairs and then
saves it in the $string variable.
$string = @"
Msg1 = Type "Windows".
Msg2 = She said, "Hello, World."
Msg3 = Enter an alias (or "nickname").
"@
This command uses the ConvertFrom-StringData cmdlet to convert the
here-string into a hashtable.
ConvertFrom-StringData $string
Name Value
---- -----
Msg3 Enter an alias (or "nickname").
Msg2 She said, "Hello, World."
Msg1 Type "Windows".
For more information about here-strings, see about_Quoting_Rules.
