Generic way of formatting groups in a HTML table in Powershell

I am looking for a generic way of removing duplicates in my HTML output generated by Powershell scripts.

For example, say I have this data in a PS script:

cls

$convertParams = @{ 
 PreContent = "<H1>HTML Format test</H1>" 
 PostContent = "<p class='footer'>$(get-date)</p>"
 head = @"
 <Title>Event Log Report</Title>
<style>

td, th { border:0px solid black; 
         border-collapse:collapse;
         white-space:pre; }
th { color:white;
     background-color:black; }
table, tr, td, th { padding: 2px; margin: 0px ;white-space:pre; }
tr:nth-child(odd) {background-color: lightgray}
table { width:95%;margin-left:5px; margin-bottom:20px;}
h2 {
 font-family:Tahoma;
 color:#6D7B8D;
}
.footer 
{ color:green; 
  margin-left:10px; 
  font-family:Tahoma;
  font-size:8pt;
  font-style:italic;
}
</style>
"@
}

function CreateCollectionItem
{
    param([int]$pvalue, [string]$pValue2, [string]$pValue3)

    $newItem = New-Object System.Object
    $newItem | Add-Member -MemberType NoteProperty -Name "Col1" -Value $pvalue
    $newItem | Add-Member -MemberType NoteProperty -Name "Col2" -Value $pValue2
    $newItem | Add-Member -MemberType NoteProperty -Name "Col3" -Value $pValue3

    return $newItem
}

$data = New-Object System.Collections.ArrayList

$data.Add((CreateCollectionItem 1 "abc" "aaaaaaaa")) | Out-Null
$data.Add((CreateCollectionItem 2 "def" "ddddddddddddddddddddddddd")) | Out-Null
$data.Add((CreateCollectionItem 2 "ghi" "gg")) | Out-Null
$data.Add((CreateCollectionItem 3 "jkl" "jj")) | Out-Null

$data | ConvertTo-Html @convertParams  | Out-File C:\temp\htmloutput.htm 

Select allOpen in new window

The result shows like this:

Is there a generic way of merging duplicate values in Col1 for example? I don't want to see repeating values. It is easier to read when values are grouped.