Powershell: How to properly count number of items in array of objects when there is only one object left in array

Question

I have an array of objects with N properties each. I perform a subset operation using Where-Object like this, for instance:

$mySubset = $myArrayOfObjects | Where-Object {($_.Property1 -eq 'ABC') -and ($_.Property2 -eq 'DEF')}

I then need to check how many objects I have in this array. I do it like this:

$mySubset.Count

When I have more than one object in the subset array, it shows number of objects. But when I have only one object left in $mySubset - it doesn't treat it as array with one element, and $mySubset.Count returns N - number of properties in each object. This is the problem. How do I convince Powershell to treat $mySubset as an array with 1 item in it in this case?

mklement0 · Accepted Answer · 2023-03-03 20:34:28Z

9

The most PowerShell-idiomatic solution is to use @(), the array-subexpression operator, which ensures that a command's output is treated as an array even if only one object is returned:

$mySubset = @($myArrayOfObjects | ...)

To get the count directly: @($myArrayOfObjects | ...).Count

You can also use an [array] type constraint - in essence, a cast placed to the left of the target variable - which doesn't require modification of the RHS:

[array] $mySubset = $myArrayOfObjects | ...

edited Mar 3, 2023 at 20:34

answered Dec 23, 2020 at 21:51

mklement0

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Comments

miguello · Accepted Answer · 2020-12-23 21:49:05Z

2

Looks like this is the way:

$mySubset = [PSObject[]]($myArrayOfObjects | Where-Object {($_.Property1 -eq 'ABC') -and ($_.Property2 -eq 'DEF')})

Or, as an one liner:

([PSObject[]]($myArrayOfObjects | Where-Object {($_.Property1 -eq 'ABC') -and ($_.Property2 -eq 'DEF')})).Count

Key point is to put parenthesis in right places, so, for instance

[PSObject[]]($myArrayOfObjects | Where-Object {($_.Property1 -eq 'ABC') -and ($_.Property2 -eq 'DEF')}).Count

would still show you N instead of "1" if number of object left is one.

answered Dec 23, 2020 at 21:49

miguello

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1 Comment

mklement0 Over a year ago

Note that there's no good reason to use [psobject] in user code; [object[]] will do or - more simply - [array]. In fact, wrapping objects in [psobject] instances can have subtle, unwanted side effects - see GitHub issue #5579.

gjh71 · Accepted Answer · 2020-12-23 21:59:30Z

1

Sometimes this behavior is convenient, but not always....

Fortunately the workaround is simple:

$mySubset = @($myArrayOfObjects | Where-Object {($_.Property1 -eq 'ABC') -and ($_.Property2 -eq 'DEF')})

Just put the result inside the array construct: @()

answered Dec 23, 2020 at 21:59

gjh71

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Comments

Adam · Accepted Answer · 2020-12-24 04:55:02Z

0

Try the following:

$mySubset=@()
$mySubset += $myArrayOfObjects | Where {$_.Property1 -eq 'ABC' -and $_.Property2 -eq 'DEF'}

$mySubset.Count

I create an empty array. I filter the $myArrayOfObjects for objects where Property1 and Property2 are "ABC" and "DEF" respectively, and I save that to $mySubset. Then I give you a count of from $mySubset.

edited Dec 24, 2020 at 4:55

Adam

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answered Dec 24, 2020 at 4:32

Esperento57

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