Script for Performance Stats - CPU/Memory (Max/Min/Avg)

We have monthly performance statistics to gather. A new requirement is for hourly CPU/Memory (Max/Min/Avg).Here's what we've come with so far:

$allhosts = @()
$allvms = @()
$hosts = Get-VMHost
$vms = Get-Vm
# connect-viserver

foreach($vmHost in $hosts){
$stats = Get-Stat -Entity $vmHost -Start (get-date).AddDays(-7) -Stat "cpu.usage.average","mem.usage.average"
$groups = $stats | Group-Object -Property {$_.Timestamp.DayOfYear,$_.Timestamp.Hour}
$groups | % {
$cpuMeasure = $_.Group | where{$_.MetricId -eq "cpu.usage.average" -and $_.Instance -eq ""} | `
Measure-Object -Property Value -Average -Maximum -Minimum
$memMeasure = $_.Group | where{$_.MetricId -eq "mem.usage.average"} | `
Measure-Object -Property Value -Average -Maximum -Minimum
$row = "" | Select HostName,Timestamp,CpuAvg,CpuMin,CpuMax,MemAvg,MemMin,MemMax
$row.HostName = $_.Group[0].Entity.Name
$row.Timestamp = $_.Group[0].Timestamp.Date.AddHours($_.Group[0].Timestamp.Hour)
$row.CpuAvg = ::Round($cpuMeasure.Average, 2)
$row.CpuMin = ::Round($cpuMeasure.Minimum, 2)
$row.CpuMax = ::Round($cpuMeasure.Maximum, 2)
$row.MemAvg = ::Round($memMeasure.Average, 2)
$row.MemMin = ::Round($memMeasure.Minimum, 2)
$row.MemMax = ::Round($memMeasure.Maximum, 2)
$allhosts += $row
}
}
$File = "C:\temp\VCScripts\Reports\Test\vmHosts_wk.csv"
$allhosts | Sort-Object -Property Timestamp | Export-Csv $File -noTypeInformation -useculture
foreach($vm in $vms){
$stats = Get-Stat -Entity $vm -Start (get-date).AddDays(-7) -Stat "cpu.usage.average","mem.usage.average"
$groups = $stats | Group-Object -Property {$_.Timestamp.DayOfYear,$_.Timestamp.Hour}
$groups | % {
$cpuMeasure = $_.Group | where{$_.MetricId -eq "cpu.usage.average" -and $_.Instance -eq ""} | `
Measure-Object -Property Value -Average -Maximum -Minimum
$memMeasure = $_.Group | where{$_.MetricId -eq "mem.usage.average"} | `
Measure-Object -Property Value -Average -Maximum -Minimum
$row = "" | Select HostName,Timestamp,CpuAvg,CpuMin,CpuMax,MemAvg,MemMin,MemMax
$row.HostName = $_.Group[0].Entity.Name
$row.Timestamp = $_.Group[0].Timestamp.Date.AddHours($_.Group[0].Timestamp.Hour)
$row.CpuAvg = ::Round($cpuMeasure.Average, 2)
$row.CpuMin = ::Round($cpuMeasure.Minimum, 2)
$row.CpuMax = ::Round($cpuMeasure.Maximum, 2)
$row.MemAvg = ::Round($memMeasure.Average, 2)
$row.MemMin = ::Round($memMeasure.Minimum, 2)
$row.MemMax = ::Round($memMeasure.Maximum, 2)
$allvms += $row
}
}
$File2 = "C:\temp\VCScripts\Reports\Test\vms_wk.csv"
$allvms | Sort-Object -Property Timestamp | Export-Csv $File2 -noTypeInformation -useculture

The problem is I'm getting the same line output for Avg/Min/Max. Any ideas?

VMware's 30 minute sampling should suffice, but given VC only holds the data for a week, I was planning to run the script every week to capture the data, then combine with the others for the montly report.