$allvms = @()
$vms = Get-Vm server1, server2, server3        
$start = "12/15/2013 06:00 PM"
$FInish = "12/15/2013 11:59 PM"
$metrics = "cpu.usage.average","mem.usage.average"
$stats = Get-Stat -Entity $vms -Start $start -Finish $Finish -Stat $metrics   
$stats | Group-Object -Property {$_.Timestamp.Day},{$_.Entity.Name} | %{
  $vmstat = "" | Select VmName, Day, MemMax, MemAvg, MemMin, CPUMax, CPUAvg, CPUMin
  $vmstat.VmName = $_.Values[1]
  $vmstat.Day = $_.Group[0].Timestamp.Date
  $cpu = $_.Group | where {$_.MetricId -eq "cpu.usage.average"} | Measure-Object -Property value -Average -Maximum -Minimum
  $mem = $_.Group | where {$_.MetricId -eq "mem.usage.average"} | Measure-Object -Property value -Average -Maximum -Minimum
  $vmstat.CPUMax = [int]$cpu.Maximum
  $vmstat.CPUAvg = [int]$cpu.Average
  $vmstat.CPUMin = [int]$cpu.Minimum
  $vmstat.MemMax = [int]$mem.Maximum
  $vmstat.MemAvg = [int]$mem.Average
  $vmstat.MemMin = [int]$mem.Minimum  
  $allvms += $vmstat
}
$allvms