Remove all group on folder

Question

I'm writing a powershell script where i create some folder. I'd like to make some group on each folder. I can add my group but all the other one by default are present too.

here is how i add my group

function GrantGroupPermission{
   param($arggroupName, $argFolder)
   [Microsoft.SharePoint.SPGroupCollection]$spgroups = $web.SiteGroups
   [Microsoft.SharePoint.SPGroup]$spgroup = $spgroups[$arggroupName]
   $sproleass=new-object Microsoft.SharePoint.SPRoleAssignment([Microsoft.SharePoint.SPPrincipal]$spgroup)
   $argFolder.BreakRoleInheritance("true")
   $sproleass.RoleDefinitionBindings.Add($web.RoleDefinitions["NoDelete"])
   $argFolder.RoleAssignments.Add($sproleass)
   $argFolder.update()
   Write-Host "Permission provided for group ", $groupName

}

and the call

$folder = $mylist.AddItem("", [Microsoft.SharePoint.SPFileSystemObjectType]::Folder,$terms.Name)
$folder.Update()
GrantGroupPermission $terms.Name $folder

I used this to remove all group but got an exception

foreach($role in $folder.Item.RoleAssignments)
         {
             $folder.RoleAssignments.Remove($role)
         }

Answer 1

Before this line:

$sproleass.RoleDefinitionBindings.Add($web.RoleDefinitions["NoDelete"])

Try writing this line:

$sproleass.RoleDefinitionBindings.RemoveAll()

It removes all role definitions for the object. Then, when you use the Add method, it should be the only role definition for that group.