How to initialize a large, multi-dimensional array in Powershell?

Question

Regarding this topic, I've so far found two questions here which relate to my question, but not fully. I have found how to initialize a large array, here. Additionally, I've found how to declare a multi-dimensional array, here. I've yet to find a solution which covers how to both declare AND initialize a multi-dimensional array. In my case, I need an array[10][10] with all elements initialized to zero. Currently I do this as follows:

$array = @(
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
)

This, of course, is completely un-scalable. From the first question, I found that $arr = @(0) * 10000 works for regular arrays, so I tried to use $array = @(@(0) * 10) * 10, and while this runs just fine, trying to access any element of this array gives me a 'Cannot modify because element is null' error.

To clarify, this code:

$array = @(
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
    @(0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
)
Write-Host "$($null -eq $array[1][5])"

returns False, where as this code:

$array = @(@(0) * 10) * 10
Write-Host "$($null -eq $array[1][5])"

returns True.

What is the definitive, correct, scalable way to declare and initialize an array with N-dimensions?

Classic PowerShell gotcha: use the comma operator: $array = ,@(,@(0) * 10) * 10, see also: Why is a leading comma required when creating an array? — iRon
– iRon, Commented Oct 18, 2021 at 8:41
Does this answer your question? Return Multidimensional Array From Function and/or Why does PowerShell flatten arrays automatically? — iRon
– iRon, Commented Oct 18, 2021 at 8:58
@iRon very useful! I actually only knew a couple of those, so reading about the rest is quite nice. Thanks! — martorad
– martorad, Commented Oct 18, 2021 at 14:33

Mathias R. Jessen · Accepted Answer · 2021-10-18 12:18:07Z

1

What is the definitive, correct, scalable way to declare and initialize an array with N-dimensions?

$2DArray = [int[,]]::new(10,10)

This will create a 10x10 2D array that you can index into like this:

$null -ne $2DArray[1,5]

For a jagged array (an array of arrays), use the unary array operator ,:

$jaggedArray = ,((0) * 10) * 10

This will create a 10-item array consisting of 10 10-item arrays of 0 that you can index into like this:

$null -ne $jaggedArray[1][5]

As mentioned in the comments, due to PowerShell's tendency to flatten any arrays, it might be better to devise a custom data type for collecting specific information:

using namespace System.Collections.Generic

class SensorSink {
  [List[int[]]]$Measurements = [List[int[]]]::new(10)

  AcceptTelemetry([int[]]$telemetry){
    if($telemetry.Count -ne 10){
      throw [ArgumentException]::new('telemetry', "Expected exactly 10 data points, received $($telemetry.Count)")
    }

    $this.Measurements.Add($telemetry)
  }
}

edited Oct 18, 2021 at 12:18

answered Oct 18, 2021 at 9:00

Mathias R. Jessen

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4 Comments

martorad Over a year ago

This is all incredibly confusing for a Powershell newbie like me. Between regular and jagged arrays, hash tables, , vs @(). That said, your solution works perfectly. You really are a Powershell guru.

Mathias R. Jessen Over a year ago

@martorad FWIW you almost never need nested arrays like this. Chances are whatever problem you're trying to solve, you'd probably be better off with an array of objects (custom or based of a class definition) describing the "inner" array values. But you'd have to tell us what you're actually trying to achieve with your 10x10 array if you what suggestions in that direction :)

martorad Over a year ago

I'm getting 10 values from 10 sensors on a microcontroller. I'm then receiving these values over Serial and reading them into my Powershell script. I receive these values 10 times, hence my 10x10 dimensionality. In truth, a regular array of 100 elements would absolutely suffice here, I decided to make it 2D purely because it looks nicer.

martorad Over a year ago

Final update, I first implemented the jaggedArray solution, which worked, but since I'm converting all my data to a JSON, it flattened it to 1 array of 100 elements. I then implemented the list of string arrays solution and that worked like a charm. Thank you!

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