How can I create each folder only once while processing a CSV in PowerShell?

The existing code also imports the CSV twice and appears to use inconsistent column names. Import it once and use the actual headers consistently. `Select-Object -ExpandProperty Folder -Unique` is fine for a simple list, but it is not enough if the same folder name can occur under different users or parents.

You can also keep a list of created folder names, but a hashtable is better because you need to retrieve the corresponding API ID. Avoid repeatedly using `+=` for large collections; hashtables or generic lists are more efficient. Whether the API rejects duplicates or creates multiple folders is an API behavior, so the script should enforce uniqueness itself rather than rely on the endpoint.

Another clear approach is to use two phases. First group the non-root rows by their folder identity, create one folder for each group, and store the returned IDs. Then loop through the original rows and create the shortcuts.

```powershell
$rows = Import-Csv $infile
$folderIds = @{}

$groups = $rows | Where-Object FOLDERNAME -ne '' |
Group-Object USERID, PARENTID, FOLDERNAME

foreach ($group in $groups) {
$first = $group.Group[0]
$response = New-RemoteFolder -Name $first.FOLDERNAME -ParentId $first.PARENTID
$key = '{0}|{1}|{2}' -f $first.USERID, $first.PARENTID, $first.FOLDERNAME
$folderIds[$key] = $response.id
}

foreach ($row in $rows) {
if ($row.FOLDERNAME -eq '') {
$destinationId = $row.PARENTID
}
else {
$key = '{0}|{1}|{2}' -f $row.USERID, $row.PARENTID, $row.FOLDERNAME
$destinationId = $folderIds[$key]
}

New-Shortcut -ParentId $destinationId -Name $row.SHORTCUTNAME -TargetId $row.TARGETID
}
```

This separates folder creation from shortcut creation and makes it impossible for the shortcut loop to create the same folder repeatedly.

You do not need a double loop over every distinct folder and every CSV row. Import the CSV once, then keep a cache of folders that have already been created. A hashtable works well because it maps a folder key to the API-generated folder ID.

The key should include every value that defines a unique folder. If folders are scoped to a user or parent, use something like "$($row.USERID)|$($row.PARENTID)|$($row.FOLDERNAME)" rather than only the folder name.

```powershell
$rows = Import-Csv -Path $infile
$folderIds = @{}

foreach ($row in $rows) {
if ($row.FOLDERNAME -eq '') {
$destinationId = $row.PARENTID
}
else {
$key = '{0}|{1}|{2}' -f $row.USERID, $row.PARENTID, $row.FOLDERNAME

if (-not $folderIds.ContainsKey($key)) {
$response = New-RemoteFolder -Name $row.FOLDERNAME -ParentId $row.PARENTID
$folderIds[$key] = $response.id
}

$destinationId = $folderIds[$key]
}

New-Shortcut -ParentId $destinationId -Name $row.SHORTCUTNAME -TargetId $row.TARGETID
}
```

The first row for a folder creates it and stores the returned ID. Later rows find that ID in the hashtable and skip the folder POST.