CODEWITHSUNDEEP
powershellhashset
mark
mark

Reputation: 62746

In Powershell how can I create a HashSet with the constructor accepting a collection?

I want to create a HashSet using the constructor accepting a collection

But none of my attempts are successful:

C:\> $c = @(1,2,3,4,5)
C:\> New-Object System.Collections.Generic.HashSet[int]
C:\> New-Object System.Collections.Generic.HashSet[int] -ArgumentList @(,$c)
New-Object : Cannot find an overload for "HashSet`1" and the argument count: "1".
At line:1 char:1
+ New-Object System.Collections.Generic.HashSet[int] -ArgumentList @(,$ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [New-Object], MethodException
    + FullyQualifiedErrorId : ConstructorInvokedThrowException,Microsoft.PowerShell.Commands.NewObjectCommand

C:\> New-Object System.Collections.Generic.HashSet[int] -ArgumentList $c
New-Object : Cannot find an overload for "HashSet`1" and the argument count: "5".
At line:1 char:1
+ New-Object System.Collections.Generic.HashSet[int] -ArgumentList $c
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [New-Object], MethodException
    + FullyQualifiedErrorId : ConstructorInvokedThrowException,Microsoft.PowerShell.Commands.NewObjectCommand

C:\> New-Object System.Collections.Generic.HashSet[int] -ArgumentList @($c)
New-Object : Cannot find an overload for "HashSet`1" and the argument count: "5".
At line:1 char:1
+ New-Object System.Collections.Generic.HashSet[int] -ArgumentList @($c ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [New-Object], MethodException
    + FullyQualifiedErrorId : ConstructorInvokedThrowException,Microsoft.PowerShell.Commands.NewObjectCommand

C:\>

Is there a way to do it?

Upvotes: 7

Views: 11861

Answers (3)

Ranga
Ranga

Reputation: 701

I realize this is a little old, but you can just cast a list to a set

> $fileTypes = [System.Collections.Generic.HashSet[String]] @(".jpg", ".txt", ".log", ".ini")
> $fileTypes
.jpg
.txt
.log
.ini
> $fileTypes.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     HashSet`1                                System.Object

> $fileTypes.Contains(".ini")
True

Upvotes: 6

Theo
Theo

Reputation: 61068

I have been fiddling with this and it seems this works:

[int[]]$c = 1,2,3,4,5
[System.Collections.Generic.HashSet[int]]::new([System.Collections.Generic.IEnumerable[int]]$c)

You can even leave out the [System.Collections.Generic.IEnumerable[int]] part here and just do

[int[]]$c = 1,2,3,4,5
[System.Collections.Generic.HashSet[int]]::new($c)

Without declaring the array as [int[]] it does not work and you'll get the error

Cannot convert the "System.Object[]" value of type "System.Object[]" to type "System.Collections.Generic.IEnumerable`1[System.Int32]".

With the typecast [int[]], the type for variable c$ is System.Int32[] and not simply System.Object[] and that is exactly what the constructor wants.

Hope that helps

Upvotes: 9

Lee_Dailey
Lee_Dailey

Reputation: 7479

apparently you cannot add the entire collection to the HashSet as such. [frown] you need to iterate over the collection and use the .Add() method. if you add a collection directly, you get that entire collection as one item in the set. ouch!

so you need something like this ... 

$HashSetTest = [System.Collections.Generic.HashSet[string]]::new()
$FileExtList = (Get-ChildItem -LiteralPath $env:TEMP -File).Extension

$FileExtList.Where({$_}).ForEach({[void]$HashSetTest.Add($_)})

$HashSetTest.GetType()
'=' * 40
$HashSetTest.Count
'=' * 40
$HashSetTest
'=' * 40

output ... 

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     HashSet`1                                System.Object
========================================
10
========================================
.csv
.zip
.txt
.json
.log
.ini
.tmp
.bmp
.js
.ani
========================================

Upvotes: -2

Related Questions