Types.md

Credit: Mark Krauss
Website: https://get-powershellblog.blogspot.com

Collection Type Guidence

When to use what

• Use Arrays if you know the element types and have a fixed length and/or known-up-front collection size that will not change.
• Use ArrayList if you have an unkown collection size with either unknown or mixed type elements.
• Use a Generic List when know the type of the elements but not the size of the collection.
• Use a HashTable if you are going to do key based lookups on a collection and don't know the object type of the elements.
• Use a Dictionary<TKey, TValue> you are going to do key based lookups on a collection and you know the type of the elements.
• Use a HashSet when you know the type of elements and just want unique values and quick lookups and assignmnets.
• Use LinkList if you are going to make large numbers of additions and subtractions to an ordered list (and have the understanding to use this type)
• Use Queue if you will build a collection that will need to be worked on First-in-first-out FIFO
• Use Stack if you will build a collection that will need to be worked Last-in-first-out LIFO
• Use SortedSet when you need a HasSet like set, but sorted (alaphbetically, for example)
• Use SortedList when you need a List, but sorted (alaphbetically, for example)
• Use SortedDictionary<TKey, TValue> when you need a Dictionary<TKey, TValue>, but sorted (alaphbetically, for example)

Avoid the following:

• Do not use Object[]
• Do not use += on Arrays. If your collection will grow or shrink, use ArrayList or List
• Do not use List for value types (int32, int64, char, etc)
• avoid using Arrays, Lists, and ArrayLists for lookup/search operations, use ditcionaries and sets instead
• Linked lists should only be considered in rediculously high volume add/remove operations to a list as the code complexity is too much for PowerShell
• Only use "sorted" types when you really need to. If you only need it for reconstituion, sorting the keys and then foreaching them can work on small collections

Examples

Arrays

https://docs.microsoft.com/en-us/dotnet/api/system.array?view=netframework-4.7.1 string array:

$Array = [string[]]@('string1','string2')

Int array:

$Array = [int[]]@(1,2,3,4,5)

ArrayList

https://docs.microsoft.com/en-us/dotnet/api/system.collections.arraylist?view=netframework-4.7.1

$ArrayList = [System.Collections.ArrayList]::new()
$null = $ArrayList.Add(1)
$null = $ArrayList.Add('String1')

List

https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1?view=netframework-4.7.1 String:

$List = [System.Collections.Generic.List[String]]::new()
$List.Add('String1')
$List.Add('String2')

Int:

$List = [System.Collections.Generic.List[Int]]::new()
$List.Add(1)
$List.Add(2)

Hashtable

https://docs.microsoft.com/en-us/dotnet/api/system.collections.hashtable?view=netframework-4.7.1

$HashTable = @{
    Key1 = "Value1"
    Key2 = "Value2"
}

Dictionary

https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2?view=netframework-4.7.1 Case Sensitive (default)

$Dictionary = [System.Collections.Generic.Dictionary[String,String]]::New()
$Dictionary['key1'] = 'Value1'
$Dictionary['key2'] = 'Value2'
# Is case sensitiveby default:
$Dictionary['Key2'] = 'Value3'

Case Insensitive:

$Comparer = [System.StringComparer]::InvariantCultureIgnoreCase
$Dictionary = [System.Collections.Generic.Dictionary[String,String]]::New($Comparer)
$Dictionary['key1'] = 'Value1'
$Dictionary['key2'] = 'Value2'
# Will repllace the key above
$Dictionary['Key2'] = 'Value3'

Example using processes and looking them up by PID:

$ProcessDict = [System.Collections.Generic.Dictionary[int,System.Diagnostics.Process]]::new()
Get-Process | ForEach-Object {
    $ProcessDict[$_.Id] = $_
}
$ProcessDict[0] | format-list *