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5. Basic Set Operations

Note

The below information is extensively based in information taken from the PowerShell® Notes for Professionals book. I plan to extend this information based on my day to day usage of the language.

A set is a collection of items which can be anything. Whatever operator we need to work on these sets are in short

the set operators and the operation is also known as set operation. Basic set operation includes Union, Interas well as addition, subtraction, etc.

5.1: Filtering: Where-Object / where /?

Filter an enumeration by using a conditional expression

Synonyms:

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Where-Object
where
?

Example:

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$names = @( "Aaron", "Albert", "Alphonse","Bernie", "Charlie", "Danny", "Ernie", "Frank")
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$names | Where-Object { $_ -like "A*" }
$names | where { $_ -like "A*" }
$names |? { $_ -like "A*" }

Returns:

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Aaron
Albert
Alphonse

5.2: Ordering: Sort-Object / sort

Sort an enumeration in either ascending or descending order

Synonyms:

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Sort-Object
sort

Assuming:

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$names = @( "Aaron", "Aaron", "Bernie", "Charlie", "Danny" )

Ascending sort is the default:

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$names | Sort-Object
$names | sort
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Aaron
Aaron
Bernie
Charlie
Danny

To request descending order:

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$names | Sort-Object -Descending
$names | sort -Descending
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Danny
Charlie
Bernie
Aaron
Aaron

You can sort using an expression.

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$names | Sort-Object { $_.length }
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Aaron
Aaron
Danny
Bernie
Charlie

5.3: Grouping: Group-Object / group

You can group an enumeration based on an expression.

Synonyms:

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Group-Object
group

Examples:

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$names = @( "Aaron", "Albert", "Alphonse","Bernie", "Charlie", "Danny", "Ernie", "Frank")
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$names | Group-Object -Property Length
$names | group -Property Length

Response:

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CountName Group
4 5 {Aaron, Danny, Ernie, Frank}
2 6 {Albert, Bernie}
1 8 {Alphonse}
1 7 {Charlie}

5.4: Projecting: Select-Object / select

Projecting an enumeration allows you to extract specific members of each object, to extract all the details, or to compute values for each object

Synonyms:

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Select-Object
SELECT

Selecting a subset of the properties:

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$dir = dir "C:\MyFolder"
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$dir | Select-Object Name, FullName, Attributes
$dir | select Name, FullName, Attributes
Name FullName Attributes
Images C:\MyFolder\Images Directory
data.txtC:\MyFolder\data.txtArchive
source.cC:\MyFolder\source.cArchive

Selecting the first element, and show all its properties:

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$d | select -first 1 *
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PSPath
PSParentPath
PSChildName
PSDrive
PSProvider
PSIsContainer
BaseName
Mode
Name
Parent
Exists
Root
FullName
Extension
CreationTime
CreationTimeUtc
LastAccessTime
LastAccessTimeUtc
LastWriteTime
LastWriteTimeUtc
Attributes