PowerShell searching matches over 3 CSVs ... slow execution - arrays

Question

I have to find matches over 3 CSVs. It is to find out whether users have AccessRights on PublicFolders in Exchange 2016. For ease of use I have already searched and stored all the needed values in 3 CSVs
"PF-Folder_Full.csv": a list of all the Publich Folders (more than 5000)
"PF-Mailboxes.csv": a list of all the users (around 50)
"PF-Permissions.csv": the result of
Get-PublicFolderClientPermission -Identity $Folder.Identity
looped through all the Public Folders (that takes ages)
I have written a script that does the job but even on a fast computer it is extremely slow because it has too loop through all the Public Folders and through all the users and then find a match for both values in the permissions
$Folders = Import-Csv -Path ".\PF-Folder_Full.csv" -Encoding Unicode
$Mailboxes = Import-Csv -Path ".\PF-Mailboxes.csv" -Encoding Unicode
$Permissions = Import-Csv -Path ".\PF-Permissions.csv" -Encoding Unicode
foreach ($Folder in $Folders) {
foreach ($Mailbox in $Mailboxes) {
$Permission = $Permissions | where {
($_.Identity -eq $Folder.Identity) -and
($_.User -eq $Mailbox.DisplayName)
}
if ($Permission) {
# some code
} else {
# some other code
}
Remove-Variable Permission
}
}
Is there a way to speed-up things? Possibly through the use of regular expressions.
I couldn't find any example that allows for extended matches between multiple arrays.

Answer 1

As Kory Gill mentioned in the comments: build two hashtables from the Identity and DisplayName properties from the first two CSVs:
$Folders = #{}
Import-Csv -Path ".\PF-Folder_Full.csv" -Encoding Unicode | ForEach-Object {
$Folders[$_.Identity] = $_
}
$Mailboxes = #{}
Import-Csv -Path ".\PF-Mailboxes.csv" -Encoding Unicode | ForEach-Object {
$Mailboxes[$_.DisplayName] = $_
}
Then process the third CSV using these hashtables for lookups:
$Permissions = Import-Csv -Path ".\PF-Permissions.csv" -Encoding Unicode
foreach ($p in $Permissions) {
if ($Folders.Contains($p.Identity) -and $Mailboxes.Contains($p.User)) {
# some code
} else {
# some other code
}
}
If you want code run just once per unique identity/user combination you could build a hashtable with the combined identity and mailbox name for filtering:
$Folders = Import-Csv -Path ".\PF-Folder_Full.csv" -Encoding Unicode |
Select-Object -Expand Identity
$Mailboxes = Import-Csv -Path ".\PF-Mailboxes.csv" -Encoding Unicode |
Select-Object -Expand DisplayName
$fltr = #{}
foreach ($f in $Folders) {
foreach ($m in $Mailboxes) {
$fltr["$f $m"] = $true
}
}
and then group the records from the third CSV:
Import-Csv -Path ".\PF-Permissions.csv" -Encoding Unicode |
Group-Object Identity, User |
ForEach-Object {
if ($fltr.Contains($_.Name)) {
# some code
} else {
# some other code
}
}