Powershell: Split Array to Pairs and Discard if Not Alternating - arrays

Question

I've got a Powershell script that uses Get-EventLog to search for events 6005, 6006, and 6008 on remote servers; after a little manipulation, it returns the results in an array.
$eventData += Get-EventLog -computerName $server_name -LogName system `
-After $prevMonthBegin -Before $prevMonthEnd |
Where-Object `
{ $_.eventid -eq 6005 -OR $_.eventID -eq 6006 -OR $_.eventID -eq 6008 } |
Select timegenerated, eventid, message, index, recordid | sort-object timegenerated
I loop through the results, and assign either down or up to the $eventData.message field and sort it again by timegenerated This returns an array like so (apologies for the formatting):
$eventData | Sort-Object timegenerated | format-table
TimeGenerated EventID Message Index
------------- ------- ------- ----- --------
8/3/2014 5:30:02 AM 6006 down 0
8/3/2014 5:30:47 AM 6005 up 0
8/24/2014 5:31:00 AM 6005 up 0
8/31/2014 2:34:59 AM 6008 down 1
8/31/2014 5:30:04 AM 6006 down 0
8/31/2014 5:30:59 AM 6005 up 0
8/31/2014 5:36:26 AM 6005 up 0
How can I create a new array from these results and arrange the TimeGenerated into up/down pairs? I would prefer to disregard the first event of the array if it is anup (so there's always down then up in the pairs), but I can work around this. It's more important to never have two consecutive down or up events, as in the example output above.
I was thinking of maybe iterating through the events and toggling a temp variable between 1 and 0 (or up and down) but that seems clunky and I just can't make anything work. It shouldn't be this hard, but that's why I'm asking for help. Let me know if providing more code would be useful; there's a quite a bit of it and I didn't want to just dump pages of it.
Here's an example of the format for the array that I would like to have. The method that I'm using pairs these events as 12121212 without looking at what types of events they are. So in the above example, the last event pair would calculate downtime where it did not exist because there were two up (6005) events.
Downtime Uptime CrashEvent?
8/3/2014 5:30:02 AM 8/3/2014 5:30:47 AM 0
8/24/2014 5:31:00 AM 8/31/2014 2:34:59 AM 0
8/31/2014 2:34:59 AM 8/31/2014 5:30:04 AM 1
8/31/2014 5:30:59 AM 8/31/2014 5:36:26 AM 0

Answer 1

Ok, this should select the last of any Down or Up event before the next of the opposite type (last Down before an Up, and last Up before a Down) which I think is what you wanted. Basically match each time the system goes down, with the time it came back up, using the last uptime/downtime notification if there are multiple in a row. I think your whole 'Discard the first of any sequential duplicate event type' is in error, but this does exactly that.
Event collection duplicated from Noah Sparks with the Select argument trimmed down a bit. Then it goes into a Switch creating a custom object whenever there is a Downtime event, and then setting the uptime for each uptime event, and outputting it whenever the next downtime event happens and starting over again.
$Events = Get-EventLog -LogName system |
Where-Object { $_.eventid -eq 6005 -OR $_.eventID -eq 6006 -OR $_.eventID -eq 6008 } |
Select timegenerated, eventid | sort-object timegenerated
$record=$null
$Output = Switch($Events){
{$_.EventID -match "600(6|8)"}{if(![string]::IsNullOrEmpty($Record.up)){$record}
$Record=[pscustomobject][ordered]#{
'Down'=$_.timegenerated
'Up'=$null
'Expected'=If($_.EventID -eq 6006){$true}else{$false}
}}
{$_.EventID -eq "6005"}{$Record.Up = $_.TimeGenerated}
}
$Output += $record
$Output
Personally I'd go with the first uptime even after a downtime event happens, but that's just me. That would take some different coding. Anyway, the results of that look like this (using my own event log entries):
Down Up Expected
---- -- --------
11/20/2013 8:47:42 AM 11/20/2013 8:49:11 AM True
11/20/2013 3:50:14 PM 12/13/2013 9:14:52 AM True
12/13/2013 9:26:21 AM 12/13/2013 9:27:42 AM False
12/13/2013 3:40:07 PM 12/13/2013 3:41:31 PM True
1/9/2014 1:13:31 PM 1/16/2014 12:38:08 PM True
1/16/2014 12:39:21 PM 1/16/2014 12:48:44 PM True
If you'll look at the second listing there, I know my computer was not down from 11/20 to 12/13, but discarding the first of sequential duplicates that is how it comes across. If we didn't do that it would show the system coming back up just one minute after going down, which is much more likely for my computer.

Answer 2

Here is an answer for how to do it that should skip duplicate entries. However, you will likely want to adjust the events you are querying otherwise you end up with down/up conditions occurring at the same time.
$Events = Get-EventLog -LogName system |
Where-Object { $_.eventid -eq 6005 -OR $_.eventID -eq 6006 -OR $_.eventID -eq 6008 } |
Select timegenerated, eventid, message, index, recordid | sort-object timegenerated
[array]$FullObj = [pscustomobject] #{
'Time' = ''
'Status' = ''
'Message' = ''
}
Foreach ($Event in $Events)
{
If ($Event.Message -eq 'The Event log service was started.' -and $fullobj.status[-1] -ne 'UP')
{
[array]$FullObj += [pscustomobject] #{
'Time' = $Event.TimeGenerated
'Status' = 'UP'
'Message' = $Event.Message
}
}
Elseif ($fullobj.status[-1] -eq 'UP' -and $fullobj.Message[-1] -notlike "The previous system shutdown*")
{
[array]$FullObj += [pscustomobject] #{
'Time' = $Event.TimeGenerated
'Status' = 'DOWN'
'Message' = $Event.Message
}
}
}
$FullObj | select time,status