Virtual Geek

When working with arrays and PSObject in PowerShell, there are several efficient methods for creating and managing array elements. Below are examples that highlight both the creation of arrays and the addition of elements in different ways. 

To create an empty array in PowerShell, you have two main options:

1. Using [System.Collections.ArrayList]
   This method initializes an ArrayList, which allows you to use the .Add() method to add elements directly without creating a new array each time.

2. Using @()
   This syntax creates a standard PowerShell array. However, adding elements with += can be less efficient since += creates a new array each time it is used.

To add elements to array.

1. Using +=
   You can add elements to a PowerShell array with the += operator, which works with different types like strings, integers, and custom objects. However, note that this approach can impact performance, especially with large arrays, as += creates a new array with each addition.

2. Using .Add() with [System.Collections.ArrayList]
   If you are using [System.Collections.ArrayList], the .Add() method can improve efficiency by adding elements directly, without reallocating the array. To prevent unwanted output in PowerShell, you can use [void] or $null = to suppress the output of operations, especially when adding elements to arrays or performing operations that return a value but don't need to display it.

$services = Get-Service | Select-Object -First 10
$running = @()
$stopped = [System.Collections.ArrayList]::new()  #[System.Collections.ArrayList]$stopped = @()
foreach ($service in $services)
{
    if ($service.Status -eq 'Running')
    {
        $running += [PSCustomObject]@{
            Status = $service.Status
            Name = $service.Name
            DisplayName = $service.DisplayName
        }
    }
    else {
        [void]$stopped.Add([PSCustomObject]@{
            Status = $service.Status
            Name = $service.Name
            DisplayName = $service.DisplayName
        })
    }
}
$running[1]
$stopped[3]

$list = New-Object System.Collections.ArrayList #'System.Collections.Generic.List[PSCustomObject]'
$list.Add([PSCustomObject]@{Name='Test1'; Value=1})
$list.Add([PSCustomObject]@{Name='Test2'; Value=2})
$list

$objectArray = [Object[]]::new(5)
$objectArray[0] = [PSCustomObject]@{ id = 1; name = "column1"; data = "data1" }
$objectArray[1] = [PSCustomObject]@{ id = 2; name = "column2"; data = "data2" }
$objectArray[2] = [PSCustomObject]@{ id = 3; name = "column3"; data = "data3" }
$objectArray[3] = [PSCustomObject]@{ id = 4; name = "column4"; data = "data4" }
$objectArray[4] = [PSCustomObject]@{ id = 5; name = "column5"; data = "data5" }
$objectArray

$arrayNumber = 5
$array = New-Object 'System.Object[]' $arrayNumber
for ($i = 0; $i -lt $arrayNumber; $i++) {
    $array[$i] = New-Object PSCustomObject -Property @{
        id   = $i
        name = "column$i"
        data = "data$i"
    }
}
$array

$arrayNumber = 5
$array = [System.Array]::CreateInstance([System.Object], $arrayNumber)
for ($i = 0; $i -lt $arrayNumber; $i++) {
    $array.SetValue([PSCustomObject]@{ id = $i; name = "column$i"; data = "data$i" }, $i)
}
$array

$newArraySize = $arrayNumber + 2
$newArray = [System.Array]::CreateInstance([System.Object], $newArraySize)
$array.CopyTo($newArray, 0)
$newArray.SetValue("New Item 1", $arrayNumber)
$newArray.SetValue("New Item 2", $arrayNumber + 1)
$newArray