PS中没有join（也没有左外join），所以最好使用for循环。参见下面的代码：

$filename1 = "c:\temp\test.csv"
$filename2 = "c:\temp\test1.csv"

$temp = Import-CSV -Path $filename1
#make $temp expandable
#$csv1 = [System.Collections.ArrayList]::new()
$csv1 = [System.Collections.ArrayList]$temp
$csv2 = Import-CSV -Path $filename2

#add column to $csv2 to indicate a match, rows with not match gets added later
foreach($row2 in $csv2)
{
   $row2 | Add-Member -NotePropertyName Found -NotePropertyValue $False
}
#add csv2 to csv1
foreach($row1 in $csv1)
{
   foreach($row2 in $csv2)
   {
      if(($row1.Entity -eq $row2.Entity) -and ($row1.Account -eq $row2.Account))
      {
         $row1 | Add-Member -NotePropertyName Amount2 -NotePropertyValue $row2.Amount
         $row2.Found = $True
         break;
      } 
   }
}
#add rows that are only in $csv2 to $csv1
foreach($row2 in $csv2)
{
   if(-not $row2.Found)
   {
         $newRow = New-Object -TypeName psobject
         $newRow | Add-Member -NotePropertyName Entity -NotePropertyValue $row2.Entity
         $newRow | Add-Member -NotePropertyName Account -NotePropertyValue $row2.Account
         $newRow | Add-Member -NotePropertyName Amount2 -NotePropertyValue $row2.Amount
         $csv1.Add($newRow)  | Out-Null
   }
}
foreach($row1 in $csv1)
{
   $amount1 = 0;
   if($row1.Amount -ne $null)
   {
      $amount1 = [int]$row1.Amount.Substring(1)
   }
   $amount2 = 0;
   if($row1.Amount2 -ne $null)
   {
      $amount2 = [int]$row1.Amount2.Substring(1)
   }
   $variance = $amount1 - $amount2
   if($variance -lt 0)
   {
      $row1 | Add-Member -NotePropertyName Variance -NotePropertyValue ('($' + [Math]::abs($variance) + ')')
   }
   else
   {
      $row1 | Add-Member -NotePropertyName Variance -NotePropertyValue ('$' + $variance)
   }
}
$csv1 | Format-Table

结果

Entity Account Amount Amount2 Variance
------ ------- ------ ------- --------
100    1001    $100   $100    $0
100    1004    $300   $200    $100
101    1002    $200   $200    $0
101    1005           $500    ($500)