Windows PowerShell 1.0 Hashtables - Revision history

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<td width="20%">[[Working with Arrays in Windows PowerShell 1.0|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Operators|Next]]</td>

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<td width="20%">[[Working with Arrays in Windows PowerShell 1.0|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Operators|Next]]</td>

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Neil at 19:42, 14 May 2009

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Neil at 13:40, 14 May 2009

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Neil: /* Accessing Hashtable Elements */

2009-03-18T18:18:24Z

‎Accessing Hashtable Elements

Neil: /* Clearing All Elements from a Windows PowerShell Hashtable */

2008-11-19T20:03:15Z

‎Clearing All Elements from a Windows PowerShell Hashtable

Neil: New page: Hash tables, also known as ''associative arrays'', are arrays where each element consists of key-value pairs. Unlike regular arrays where elements are accessed using an index, the values i...

2008-11-19T19:43:31Z

New page: Hash tables, also known as ''associative arrays'', are arrays where each element consists of key-value pairs. Unlike regular arrays where elements are accessed using an index, the values i...

New page

Hash tables, also known as ''associative arrays'', are arrays where each element consists of key-value pairs. Unlike regular arrays where elements are accessed using an index, the values in a hash table are accessed using the value's respective key.

== Creating PowerShell Hashtables ==

Hash tables are represented in Windows PowerShell by the .NET System.Collections.Hashtable object and are created using key and value pairs enclosed in @{ and } characters. Each key is assigned a value using the '=' sign, and multiple pairs are separated by semi-colons (;):

<pre>
PS C:\Users\Administrator> $book = @{ isbn = 12312312; title = "The Power of Widgets"; author = "Smith, John" }
</pre>

In the above example, a hashtable is created with three values, each accessible using a key (''isbn'', ''title'' and ''author'').

An empty hashtable may be created so that elements may be added at a later time as follows:

<pre>
PS C:\Users\Administrator> $myhashtable = @{}
</pre>

== Accessing Hashtable Elements ==

All the entries of a hashtable may be accessed simultaneously simply by referencing the hashtable variable name:

<pre>
PS C:\Users\Administrator> $book

Name Value
---- -----
author Smith, John
isbn 12312312
title The Power of Widgets
</pre>

Unlike standard arrays, hashtable elements are accessed using the keys assigned at creation time rather than by an index value. The key can be used either with object property dot-notation as follows:

<pre>
PS C:\Users\Administrator> $book.author
Smith, John
</pre>

or using the square brackets ([]) array accessor notation, using the key rather than an index value. When using this technique it is important to note that the key must be enclosed in double quotes:

<pre>
PS C:\Users\Administrator> $book["author"]
Smith, John
</pre>

One advantage of this particular approach is that multiple elements may be extracted in a single command using a comma separated list of keys:

<pre>
PS C:\Users\Administrator> $book["author","title"]
Smith, John
The Power of Widgets
</pre>

== Modifying Windows PowerShell Hashtable Elements ==

The value of a hashtable element may be changed using either object property dot-notation or array accessor techniques, the assignment operator (=) and the new value. The following commands change the values of the ISBN and title elements respectively:

<pre>
PS C:\Users\Administrator> $book["isbn"] = 432234234
PS C:\Users\Administrator> $book.author = "Fred Wilson"
PS C:\Users\Administrator> $book

Name Value
---- -----
author Fred Wilson
isbn 432234234
title The Power of Widgets
</pre>

== Adding Elements to a Windows PowerShell Hashtable ==

New elements may be added to a hashtable using both object property and array acessor notation together with the new key and value pair. To add ''publisher'' and ''price'' elements to our ''$book'' hashtable, therefore, the following commands may be used:

<pre>
PS C:\Users\Administrator> $book.publisher = "Pulp Media"
PS C:\Users\Administrator> $book["price"] = 10.34
PS C:\Users\Administrator> $book

Name Value
---- -----
author Fred Wilson
publisher Pulp Media
price 10.34
isbn 432234234
title The Power of Widgets
</pre>

== Removing Elements from a Windows PowerShell Hashtable ==

Unwanted elements may be removed from a hashtable using the ''remove()'' method of the object, referencing the key associated with the element to be removed. For example, to remove the ''price'' element from our ''$book'' hashtable:

<pre>
PS C:\Users\Administrator> $book.remove("price")
PS C:\Users\Administrator> $book

Name Value
---- -----
author Fred Wilson
publisher Pulp Media
isbn 432234234
title The Power of Widgets
</pre>

== Clearing All Elements from a Windows PowerShell Hashtable ==

In the event that all elements are to be removed from a Windows PowerShell hashtable, an fast alternative to removing each element one by one is to the use the ''clear()'' method as demonstrated below:

<pre>
PS C:\Users\Administrator> $book.Count
4
PS C:\Users\Administrator> $book.Clear()
PS C:\Users\Administrator> $book.Count
0
</pre>

== Listing Hashtable Count, Keys and Values ==

The number of elements in a hashtable may be accessed via the ''count'' property:

<pre>
PS C:\Users\Administrator> $book.Count
4
</pre>

The keys contained within a hashtable can be listed at any time using the ''keys'' property:

<pre>
PS C:\Users\Administrator> $book.keys
author
publisher
isbn
title
</pre>

Similarly, the actual values may be listed through the use of the ''values'' property as illustrated below:

<pre>
PS C:\Users\Administrator> $book.values
Fred Wilson
Pulp Media
432234234
The Power of Widgets
</pre>

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 == Adding Elements to a Windows PowerShell Hashtable ==
-New elements may be added to a hashtable using both object property and array acessor notation together with the new key and value pair. To add ''publisher'' and ''price'' elements to our ''$book'' hashtable, therefore, the following commands may be used:
+New elements may be added to a hashtable using both object property and array accessor notation together with the new key and value pair. To add ''publisher'' and ''price'' elements to our ''$book'' hashtable, therefore, the following commands may be used:
 <pre>
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 == Clearing All Elements from a Windows PowerShell Hashtable ==
-In the event that all elements are to be removed from a Windows PowerShell hashtable, an fast alternative to removing each element one by one is to the use the ''clear()'' method as demonstrated below:
+In the event that all elements are to be removed from a Windows PowerShell hashtable, a fast alternative to removing each element one by one is to the use the ''clear()'' method as demonstrated below:
 <pre>
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 Elements in two or more hashtables may be combined using a variety of techniques. One important point to note is that the combination can only be performed by PowerShell if there are no duplicated keys in the hashtables. If duplicate keys are found the operation will fail.
-The elements in one hashtable may be added those in another hashtable using the += operator. In the following example, the elements in ''$book2'' are added to ''$book1'':
+The elements in one hashtable may be added to those in another hashtable using the += operator. In the following example, the elements in ''$book2'' are added to ''$book1'':
 <pre>
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 The Power of Widgets
 </pre>

← Older revision		Revision as of 13:40, 14 May 2009
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		+	<td width="20%">[[Working with Arrays in Windows PowerShell 1.0\|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials\|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Operators\|Next]]</td>
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		+	<td width="20%">Working with Arrays in Windows PowerShell 1.0<td align="center"><td width="20%" align="right">Basic Windows PowerShell 1.0 Operators</td>
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	Hash tables, also known as ''associative arrays'', are arrays where each element consists of key-value pairs. Unlike regular arrays where elements are accessed using an index, the values in a hash table are accessed using the value's respective key.		Hash tables, also known as ''associative arrays'', are arrays where each element consists of key-value pairs. Unlike regular arrays where elements are accessed using an index, the values in a hash table are accessed using the value's respective key.

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 == Accessing Hashtable Elements ==
+<google>ADSDAQBOX_FLOW</google>
 All the entries of a hashtable may be accessed simultaneously simply by referencing the hashtable variable name:

← Older revision		Revision as of 20:03, 19 November 2008
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	PS C:\Users\Administrator> $book.Count		PS C:\Users\Administrator> $book.Count
	0		0
		+	</pre>
		+
		+	== Combining Hashtables ==
		+
		+	Elements in two or more hashtables may be combined using a variety of techniques. One important point to note is that the combination can only be performed by PowerShell if there are no duplicated keys in the hashtables. If duplicate keys are found the operation will fail.
		+
		+	The elements in one hashtable may be added those in another hashtable using the += operator. In the following example, the elements in ''$book2'' are added to ''$book1'':
		+
		+	<pre>
		+	PS C:\Users\Administrator> $book1 += $book2
		+	</pre>
		+
		+	Alternatively, a new hashtable may be created comprised of the elements in multiple other hashtables using the + operator. For example, the following command creates a new hashtable named ''$book4'' which contains copies of all the elements in the ''$book1'', ''$book2'' and ''$book3'' hashtables:
		+
		+	<pre>
		+	PS C:\Users\Administrator> $book4 = $book1 + $book2 + $book3
	</pre>		</pre>