Powershell Grouping acting differently in different versions

Question: How do I write this so it gives the same result in v4 and v5?

I am trying to group the following dataset by SiteCode.

I have a dataset as follows [Array of Hashes]:

Assume AppointmentId is always unique

---

$groupedDataset = @{}

$dataset = @(
    @{
        Program          = "x"
        AppointmentId    = "1234567891"
        AdminDate        = "x"
        CountryName      = "x"
        SiteCode         = "x1111"
        DateRequested    = "x"
        SubjectID        = "x"
        AccountID        = "x"  
    },
    @{
        Program          = "x"
        AppointmentId    = "1234567892"
        AdminDate        = "x"
        CountryName      = "x"
        SiteCode         = "x1112"
        DateRequested    = "x"
        SubjectID        = "x"
        AccountID        = "x"  
    },
    @{
        Program          = "x"
        AppointmentId    = "1234567893"
        AdminDate        = "x"
        CountryName      = "x"
        SiteCode         = "x1113"
        DateRequested    = "x"
        SubjectID        = "x"
        AccountID        = "x"  
    },
    @{
        Program          = "x"
        AppointmentId    = "1234567894"
        AdminDate        = "x"
        CountryName      = "x"
        SiteCode         = "x1111"
        DateRequested    = "x"
        SubjectID        = "x"
        AccountID        = "x"  
    }
)

When I run the following code below in PS Version: 5.1

$dataset |
    ForEach-Object { [PSCustomObject]$_ } |
    Group-Object -Property SiteCode |
    ForEach-Object {
        $groupedDataset[$_.Name] = $_.Group
    }

It returns the result I require:

Name                           Value                                           
----                           -----                                           
x1113                        {@{SiteCode=x1113; Program=x; Appointment...
x1111                        {@{SiteCode=x1111; Program=x; Appointment...
x1112                        {@{SiteCode=x1112; Program=x; Appointment...

---

When I run the exact code in PS Version: 4.0 it returns the following:

Name                           Value                                           
----                           -----                                           
                               {System.Collections.Hashtable, System.Collect...

In PowerShell v5.0 improvements have been made, eg. PSCustomObject casting, which is in your script

ForEach-Object { [PSCustomObject]$_ }

Try doing it the old school way and instead of building a hashtable yourself, use the one returned by the groupby.

$groupedDataset = $dataset |
    ForEach-Object {
         [PSCustomObject]@{
            Program          = $_.Program
            AppointmentId    = $_.AppointmentId
            AdminDate        = $_.AdminDate
            CountryName      = $_.CountryName
            SiteCode         = $_.SiteCode
            DateRequested    = $_.DateRequested
            SubjectID        = $_.SubjectID
            AccountID        = $_.AccountID
        }
    } |
    Group-Object -Property SiteCode -AsHashTable

This results in

$groupedDataset | out-host

Count Name  Group                                                                                                                                                                                        
----- ----- ------                                                                                                                                                                               
2     x1111 {@{Program=x; AppointmentId=1234567891; AdminDate=x; CountryName=x; SiteCode=x1111; DateRequested=x; SubjectID=x; AccountID=x}, @{Program=x; AppointmentId=1234567894; AdminDate=x; CountryN...
1     x1112 {@{Program=x; AppointmentId=1234567892; AdminDate=x; CountryName=x; SiteCode=x1112; DateRequested=x; SubjectID=x; AccountID=x}}                                                                
1     x1113 {@{Program=x; AppointmentId=1234567893; AdminDate=x; CountryName=x; SiteCode=x1113; DateRequested=x; SubjectID=x; AccountID=x}