Combine CSV columns from multiple sources into one

Question

Hi, 
I am trying to import column from one CSV file and output it into additional columns on a Get-MailboxStatistics | Export-CSV command. The issue with the script I have created is that when use an Expression to create the new column it outputs all of the items
in the column from the import CSV into one row. See script below, I have highlighted the expressions that are not working.
Any assistance would be appreciated. 
[Array]$Global:NotesMailSizeMaster = (Import-Csv c:\usermigration.csv).MailSizeMaster
[Array]$Global:NotesMailSizeRefresh = (Import-Csv c:\usermigration.csv).MailSizeRefresh
[Array]$Global:UserAlias = (Import-Csv c:\usermigration.csv).Alias
if (!(Get-PSSnapin |
Where-Object { $_.name -eq "Microsoft.Exchange.Management.PowerShell.Admin" }))
ADD-PSSnapin Microsoft.Exchange.Management.PowerShell.Admin
$Output = ForEach ($Alias in $UserAlias)
{ Get-MailboxStatistics $Alias | select-object DisplayName, ServerName, StorageGroupName, Database, @{ Name = "TotalItemSize"; expression = { $_.TotalItemSize.Value.ToMB() } },
@{ Name = "NotesMailSize(PreRefresh)"; expression = { $NotesMailSizeMaster } }, @{
Name = "NotesMailSize(PostRefresh)"; expression = { $NotesMailSizeRefresh }
$filename = (Get-Date).ToString("yyyyMMdd")
$Output | export-csv -Path c:\"$filename-mailboxstats.csv" -NoTypeInformation

Answer 1

There's a lot wrong with this script:
1.  You're importing the same file 3x; you should import one and reference the things you need out of it.
2.  If the CSV has more than one row in it, your .notation you're using to access the MailSizeMaster, MailSizeRefresh, and Alias properties is used incorrectly.  If you are trying to reference each of those properties from an array of different entries,
the proper way would be:
$Import = @(Import-Csv C:\usermigration.csv)
$MailSizeMaster = $Import | Select-Object MailSizeMaster
OR
$MailSizeMaster = $Import | Select-Object -Expand MailSizeMaster
...the "OR" is not PowerShell. 
3.  I don't know if you can concatenate different objects with the select-object cmdlet like you are.  However, what you could do is create a custom object to load the values into and then output that object:
$filename = (Get-Date).ToString("yyyyMMdd")
foreach ($item in $Import) {
$MS = Get-MailboxStatistics $item.Alias
New-Object PSObject -Property @{
'DisplayName' = $MS.DisplayName
'ServerName' = $MS.ServerName
'StorageGroupName' = $MS.StorageGroup
'Database' = $MS.Database
'NotesMailSizePre' = $item.MailSizeMaster
'NotesMailSizePost' = $item.MailSizeRefresh
} | Select-Object DisplayName,ServerName,StorageGroupName,Database,NotesMailSizePre,NotesMailSizePost | Export-Csv -NoTypeInformation "C:\$($filename)-mailboxstats.csv"