$InStuff = Import-Csv 'M:MyDocscriptlogfilesOutput_18Marstreams_E1WAF2_OUTPUT.csv'
$TargetPropertyList = $InStuff[0].PSObject.Properties.Name.Where({$_ -ne 'TimeStamp'})

$GroupedInStuff = $InStuff |
    Group-Object -Property TimeStamp

$Results = foreach ($GIS_Item in $GroupedInStuff) {
    $HighestValues = [ordered]@{
        TimeStamp = $GIS_Item.Name
    }
    foreach ($TPL_Item in $TargetPropertyList) {
        $TempHiVal = [Math]::Round(($GIS_Item.Group.$TPL_Item.ForEach({[int]$_}) | Measure-Object -Average).Average)
        $HighestValues.Add($TPL_Item, $TempHiVal)
    }

    [PSCustomObject]$HighestValues
}

$Results = $Results | Sort-Object -Property {[DateTime]$_.TimeStamp}

$InStuff = Import-Csv 'M:MyDocscriptlogfilesOutput_18Marstreams_E1WAF2_OUTPUT.csv'
$TargetPropertyList = $InStuff[0].PSObject.Properties.Name.Where({$_ -ne 'TimeStamp'})

$GroupedInStuff = $InStuff |
    Group-Object -Property TimeStamp

$Results = foreach ($GIS_Item in $GroupedInStuff) {
    $HighestValues = [ordered]@{
        TimeStamp = $GIS_Item.Name
    }
    foreach ($TPL_Item in $TargetPropertyList) {
        $TempHiVal = [Math]::Round(($GIS_Item.Group.$TPL_Item.ForEach({[int]$_}) | Measure-Object -Average).Average)
        $HighestValues.Add($TPL_Item, $TempHiVal)
    }

    [PSCustomObject]$HighestValues
}

$Results = $Results | Sort-Object -Property {[DateTime]$_.TimeStamp}

, 2

$csv = import-csv C:temptest.csv
$Averages = New-Object System.Collections.ArrayList

Foreach($object in ($csv | Group-Object timestamp)) {

    $Averages.Add([pscustomobject]@{
        timestamp = $object.Name
        abc = ($object.group | Select-Object -ExpandProperty abc | Measure-Object -Average).Average
        a = ($object.group | Select-Object -ExpandProperty a | Measure-Object -Average).Average
        b = ($object.group | Select-Object -ExpandProperty b | Measure-Object -Average).Average
        c = ($object.group | Select-Object -ExpandProperty c | Measure-Object -Average).Average
        d = ($object.group | Select-Object -ExpandProperty d | Measure-Object -Average).Average
        e = ($object.group | Select-Object -ExpandProperty e | Measure-Object -Average).Average
        f = ($object.group | Select-Object -ExpandProperty f | Measure-Object -Average).Average
        g = ($object.group | Select-Object -ExpandProperty g | Measure-Object -Average).Average
        })
}

PS H:> $Averages


timestamp : 6/4/2019
abc       : 6811.33333333333
a         : 3129
b         : 10.6666666666667
c         : 2680
d         : 1522.66666666667
e         : 1184
f         : 0
g         : 9.33333333333333

timestamp : 6/5/2019
abc       : 6783.33333333333
a         : 3098
b         : 6.66666666666667
c         : 2698.66666666667
d         : 1320
e         : 686.666666666667
f         : 0
g         : 1.33333333333333