Inserting values into an array in PowerShell

Question

I have a function that recursively examines an XML object loaded from file. I can retrieve the node data just fine, but when I try to insert the object with user data using the .Insert method, I get the error:

Exception calling "Insert" with "2" argument(s): "Insertion index was out of range. Must be non-negative and less than or equal to size. Parameter name: index"

If I replace the object values with simple string test values, insert works as expected. However, I'm using an object for each pass of the loop, and building up a large object to output to a file. Here is the simplified excerpt:

# some dummy values #
$drives = "value1","value2"
[System.Collections.ArrayList]$DriveObject = @()
$DriveObject.Add("$drives") | Out-Null

# some dummy users #
$FilterUser = "User1","User2"
[System.Collections.ArrayList]$UserObject = @()
$UserObject.Add("$FilterUser") | Out-Null

# insert user object into drive object #
$DriveObject.Insert($DriveObject.LastIndexOf('value2'),$UserObject)

# output #
$DriveObject

Mathias R. Jessen · Accepted Answer · 2021-09-09 16:10:59Z

3

When you call $DriveObject.Add("$drives"), the expression "$drives" creates a new string, so $DriveObject doesn't actually contain two separate values, it contains only a single string "value1 value2".

Use the AddRange() method to add multiple items to the ArrayList at a time:

# some dummy values #
$drives = "value1","value2"
[System.Collections.ArrayList]$DriveObject = @()
$DriveObject.AddRange($drives) | Out-Null

# some dummy users #
$FilterUser = "User1","User2"
[System.Collections.ArrayList]$UserObject = @()
$UserObject.AddRange($FilterUser) | Out-Null

# insert user object into drive object #
$DriveObject.Insert($DriveObject.LastIndexOf('value2'),$UserObject)

# output #
$DriveObject

answered Sep 9, 2021 at 16:10

Mathias R. Jessen

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1 Comment

TenBob Over a year ago

Thank you! I also noticed that the double quotes around the value cause errors, which you removed in your modification. PowerShell syntax can be awkward! Thanks again

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