How do I create an empty array of arrays in Powershell?

Question

I want to create an empty array of arrays in Powershell to hold "tuples" of values (arrays are immutable).

Therefore I try something like:

The type of $arr is Object[]. I've read that += @(1,2) appends the given element (i.e. @(1,2)) to $arr (actually creates a new array). However, in this case it seems that the arrays are concatenated, why?

$arr = @()
$arr += @(1,2)
$arr.Length // 2 (not 1)

If I do as follows, it seems that $arr contains the two arrays @(1,2),@(3,4), which is what I want:

$arr = @()
$arr += @(1,2),@(3,4)
$arr.Length // 2

How do I initialize an empty array of arrays, such that I can add one subarray at a time, like $arr += @(1,2)?

lit · Accepted Answer · 2018-04-21 19:00:15Z

18

The answer from Bruce Payette will work. The syntax seems a bit awkward to me, but it does work. At least it is not Perl.

Another way to do this would be with an ArrayList. To me, this syntax is more clear and more likely to be understood by another developer (or myself) in six months.

[System.Collections.ArrayList]$al = @()

$al.Add(@(1,2))
$al.Add(@(3,4))

foreach ($e in $al) {
    $e
    $e.GetType()
}

answered Apr 21, 2018 at 19:00

lit

16.5k11 gold badges79 silver badges146 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Bruce Payette · Accepted Answer · 2018-04-21 12:10:09Z

6

The + operator concatenates arrays. To add an array as a single element, prefix the element to add with a comma. Something like @() + , (1,2) + , (3, 4).

answered Apr 21, 2018 at 12:10

Bruce Payette

2,67912 silver badges8 bronze badges

Comments

Slogmeister Extraordinaire · Accepted Answer · 2018-09-25 19:41:43Z

3

As far as I can tell, you can't do it natively in PowerShell, nor can you do it with the [System.Array] type. In both cases, you seem to need to define both the length and the type of the array. Because I wanted a completely empty array of arrays, with the ability to store any type of value in the array, I did it this way.

$x=[System.Collections.ArrayList]::new()
$x.Count
$x.GetType()

$x.Add([System.Collections.ArrayList]::new()) > $null
$x.Count
$x[0].Count
$x[0].GetType()

$x[0].Add("first element") > $null
$x.Count
$x[0].Count
$x[0][0]

answered Sep 25, 2018 at 19:41

Slogmeister Extraordinaire

3,2462 gold badges32 silver badges45 bronze badges

Comments

Darin · Accepted Answer · 2024-05-14 17:03:58Z

0

An array of untyped arrays, having a length of 0:

$UntypedAoAs = [array[]]::new(0)
$UntypedAoAs.Length # Returns 0

Appending to an array of untyped arrays:

$UntypedAoAs += , ('a', 1)
$UntypedAoAs += , ('b', 2)
$UntypedAoAs += , ('c', 3)
$UntypedAoAs.Length     # Returns 3
$UntypedAoAs[0]         # Returns 'a' and 1
$UntypedAoAs[0].Length  # Returns 2
$UntypedAoAs[2][0]      # Returns 'c'

Verifying the type of elements:

$UntypedAoAs[0][0].GetType() # String type
$UntypedAoAs[0][1].GetType() # Int32 type

You can replace [array[]] with [string[][]], but it appears that this will NOT restrict/prevent appending arrays of any type you want.

answered May 14, 2024 at 17:03

Darin

2,4381 gold badge20 silver badges20 bronze badges

Collectives™ on Stack Overflow

How do I create an empty array of arrays in Powershell?

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related