Process and compare records in single collection without repeating


can you advise what should I search for in documentation. I do not know how to call what I am trying to do.
I have a $collection with $record and need to process each to $records a compare it. But I do not want to compare same records and repeat the comparison.
Dummy example of code:

foreach ($record in $collection) {
$start = $record.time
$label1 = $record.label
foreach ($otherrecord in $collection) {
$end = $otherrecord.time
$label2 = $otherrecord.label
$howlong = (New-TimeSpan -Start $start -End $end).totalhours
if ($howlong -gt 24) {
write-host "$label1 and $label2 with more than 24 hours time difference."

With the code above, it would compare:

A-A (do not want)
B-A (do not want)
B-B (do not want)
C-A (do not want)
C-B (do not want)
C-C (do not want)

It does not matter with 3 records, but I have collection with 80 000+ records. Is there a function or some trick for this? What should I look for?

Thank you


How about this?

foreach ($item in $collection){
    $collection | 
        Where-Object {($_.time - $item.time).TotalHours -gt 24} |
            foreach-object {"{0} and {1} with more than 24 hours" -f $item.label, $_.label}  


You have two sources with matching labels? Normally you would want to do some kind of join operation on the other recordset (e.g. Label) and build an object:

$record = @()
$record += [pscustomobject]@{Label='A-A';Time=(Get-Date)}
$record += [pscustomobject]@{Label='A-B';Time=(Get-Date)}

$otherrecord = @()
$otherrecord += [pscustomobject]@{Label='A-A';Time=(Get-Date).AddDays(2)}
$otherrecord += [pscustomobject]@{Label='A-B';Time=(Get-Date).AddHours(2)}

$results = foreach ($r in $record) {
    $match = $otherRecord | Where{$_.Label -eq $r.Label}

    $r | Select-Object Label, 
                       @{Name='Hours';Expression={[math]::Round((New-TimeSpan -Start $_.Time -End $match.Time).TotalHours)}}

$results | Where{$_.Hours -gt '24'}

Once you have the object, you can execute a filter on the results:

PS C:\Users\rasim> $results

Label StartTime            EndTime               Hours
----- ---------            -------               -----
A-A   12/8/2020 3:20:14 PM 12/10/2020 3:20:14 PM    48
A-B   12/8/2020 3:20:14 PM 12/8/2020 5:20:14 PM      2

PS C:\Users\rasim> c:\Users\rasim\Desktop\temp.ps1

Label StartTime            EndTime               Hours
----- ---------            -------               -----
A-A   12/8/2020 3:25:52 PM 12/10/2020 3:25:52 PM    48

While you can output a string or log, you are then reading it manually. If you use an object approach, you can see all of that data and can do comparisons and exports such as a csv.

To me it is simplest to use a Queue object. You can Dequeue() (remove) the first object during each run to ensure no repeats.

$queue = [System.Collections.Queue]::new($collection)

while ($queue.Count) {
    $top = $queue.Dequeue()
    $queue.ToArray() | Foreach-Object {
        if (($top.Time - $_.Time).Duration().TotalSeconds -gt 86400) {
            "{0} and {1} with more than 24 hours time difference" -f $top.label,$_.Label

This is not going to be an efficient process without have presorted data or using another tool built for bulk comparisons/joins.

Thank you guys.

I think I found solution on my own. It is primitive, but it works.

$collection2 = $collection1
$collection2 = {$collection2}.invoke()
foreach ($collrow1 in $collection1) {
if ($null -ne $collection2) {
foreach ($collrow2 in $collection2) {
... compare values ...


Thank you all. I am going to check your ideas anyway.