Selecting Distinct Items within Array using PowerShell and Linq - arrays

Question

I have been banging my head on this problem for a few hours.
I have a multi-dimensional array and I need to select the unique items based on two "columns".
Is there an efficient .Net or otherwise way to do this and achieve the desired output?
The data looks something like:
ComputerName, IPAddress, MacAddress, FirstObserved
I would like to determine unique values based on MacAddress and ComputerName and keep the unique value based on the oldest FirstObserved date.
I have tried the PowerShell ways of doing this but it's horribly slow to say the least.
$data | Group-Object -Property ComputerName,MacAddress | ForEach-Object{$_.Group | Sort-Object -Property FirstObserved | Select-Object -First 1}
In a perfect world I would have a list of items no duplicates with the oldest entry based on FirstObserved date.

Answer 1

You can implement the grouping manually with a hashtable:
$FirstObserved = #{}
Import-Csv .\data.csv |ForEach-Object {
$key = $_.Computername,$_.MacAddress -join ','
$date = $_.FirstObserved -as [datetime]
# Check if we already have an entry for this Name + MAC combo
if($FirstObserved.Contains($key))
{
# Make sure the current date is older than what we have already
if($FirstObserved[$key] -gt $date)
{
$FirstObserved[$key] = $date
}
}
else
{
# First instance of the Name + MAC combo, save the date
$FirstObserved[$key] = $date
}
}
Now you can eaily look up the first date for a combination with:
$FirstObserved["Computer-01,11:22:33:44:55:66"]
If you want to export the list to another csv, all you need to do is turn the key-value pairs of the hashtable into objects:
$FirstObserved |Select-Object #{Name='Identity';Expression={$_.Key}},#{Name='FirstObserved';Expression={$_.Value}} |Export-Csv -Path output.csv