param(
    [Parameter(Mandatory = $false, Position = 1)]
    [int]
    $Keep = 100
)

Get-AzureRmResourceGroup | ForEach-Object {
    $ts = (Get-AzureRmResourceGroupDeployment -ResourceGroupName $_.ResourceGroupName |
            Sort-Object Timestamp -Descending |
            Select-Object -First $Keep |
            Select-Object -Last 1).Timestamp
    if ($ts) {
        Write-Host "delete from" $_.ResourceGroupName "older than " $ts
        Get-AzureRmResourceGroupDeployment -ResourceGroupName $_.ResourceGroupName |
            Where-Object {$_.Timestamp -lt $ts} |
            Remove-AzureRmResourceGroupDeployment
    }
}