Formatting Compare-Object Ouput

Question

Hello all and good morning.

I'm just looking to see if I can format the output of Compare-Object into a pscustomobject. I have taken a look at the following questions that are similar:

• PowerShell Compare-Object SideIndicator
• Compare-Object Format Output
• Compare-Object Output Format

...but, I just don't seem to grasp the concept of it. I hate to ask questions that are already have been answered that correlate to this but, im just a bit confused. The 3rd link was the only one I was beginning to understand but, still got lost in the sauce.

Just looking to separate the output based off the SideIndicator return property.

$Reference = Get-Content "C:\Users\Abe\Desktop\onj1.txt"
$Difference = Get-Content "C:\Users\Abe\Desktop\onj2.txt"


Compare-Object -ReferenceObject $Reference -DifferenceObject $Difference -IncludeEqual | Tee-Object -Variable CompareObject | Out-Null
$compareObject | Foreach { 
$ONJ1 = $_.SideIndicator -eq "<=" | Select $_.InputObject
$ONJ2 = $_.SideIndicator -eq "=>" | Select $_.InputObject
$Both = $_.SideIndicator -eq "==" | Select $_.inputobject

    [pscustomobject]@{
        ONJ1 = $ONJ1
        ONJ2 = $ONJ2
        Both = $Both
                }
        } 

Unfortunately, all 3 columns return the same output and im assuming its because im selecting the InputObject property but, it grabs them all.

EDIT: As explained by Zett42

$Reference = Get-Content "C:\Users\Abe\Desktop\onj1.txt"
$Difference = Get-Content "C:\Users\Abe\Desktop\onj2.txt"


Compare-Object -ReferenceObject $Reference -DifferenceObject $Difference -IncludeEqual | Tee-Object -Variable CompareObject | Out-Null

$null = [array]$ONJ1 = $compareObject | Where-Object {$_.SideIndicator -eq "<="} | Select-Object -ExpandProperty InputObject
$null = [array]$ONJ2 = $compareObject | Where-Object {$_.SideIndicator -eq "=>"} | Select-Object -ExpandProperty InputObject
$null = [array]$Both = $compareObject | Where-Object {$_.SideIndicator -eq "=="} | Select-Object -ExpandProperty InputObject


For($i=0; $i -lt ($ONJ1.Count + $ONJ2.Count + $Both.Count); $i++){
    [pscustomobject]@{
        ONJ1 = $ONJ1[$i]
        ONJ2 = $ONJ2[$i]
        Both = $Both[$i]
                }
        } 

Answer 1

You are grabbing the formatted output strings, not the actual data from Compare-Object. The formatted output will be hard to process, because it is just unstructured strings. Store direct output of Compare-Object into a variable, without piping to other cmdlets. Then you do further processing based on that data.

$reference = 'foo', 'bar', 'baz', 'bim'
$difference = 'bim', 'fop', 'bar'

$compareObject = Compare-Object -ReferenceObject $Reference -DifferenceObject $Difference -IncludeEqual 

Then separate the result based on the SideIndicator:

[array] $left  = $compareObject | Where-Object SideIndicator -eq '<=' | 
                                  Select-Object -ExpandProperty InputObject
[array] $right = $compareObject | Where-Object SideIndicator -eq '=>' | 
                                  Select-Object -ExpandProperty InputObject
[array] $both  = $compareObject | Where-Object SideIndicator -eq '==' |
                                  Select-Object -ExpandProperty InputObject

The variable $left is an array that contains only items that are in $Reference, $right contains only items that are in $Difference and $both obviously contains items that are in both $Reference and $Difference.

_{NOTE: I've explicitly set the type of the variables to [array] so we can treat single element output the same as multiple elements. Applying the index operator to a single string would select a single character, whereas applying the index operator to an array of strings would output a single string. By explicitly setting the variable type to [array] we handle both cases without extra code.}

Now we can do further processing based on the separated results, e. g. stuffing them into a single array of [PSCustomObject]:

# Determine the total number of rows we need. -1 to make it a valid array index.
$maxIndex = ( $left.Count, $right.Count, $both.Count | Measure-Object -Maximum ).Maximum - 1

foreach( $i in 0..$maxIndex ) {
    [pscustomobject]@{
        ONJ1 = if( $i -lt $left.Count )  { $left[ $i ] }  else { $null }
        ONJ2 = if( $i -lt $right.Count ) { $right[ $i ] } else { $null }
        Both = if( $i -lt $both.Count )  { $both[ $i ] }  else { $null }
    }
}

The if/else on the right-hand side of an assignment is called conditional assignment (aka ternary operator). As each of the arrays $left, $right and $both may have different size (less than $maxIndex), we need to make sure to not "overshoot" and use an invalid index.

Actually this is only necessary when using strict mode >= v3.0 (e. g. Set-StrictMode -Version 3.0), in which case you would get a fatal "index out of bounds" error when specifying an invalid array index. Without strict mode, you could write ONJ1 = $left[ $i ] without checking the index. Personally I prefer to know that my indices are always correct and not rely on the programming language to silently "fix" my errors.

Output:

ONJ1 ONJ2 Both
---- ---- ----
foo  fop  bar
baz       bim

Answer 2

Unsure what you expect as formatted output, but perhaps something ;ike this?

onj1.txt

Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor.

onj2.txt

Lorem ipsum dolor sit amet, 
sed do eiusmod tempor.

$Reference = Get-Content "C:\Users\Abe\Desktop\onj1.txt"
$Difference = Get-Content "C:\Users\Abe\Desktop\onj2.txt"

$compare = Compare-Object -ReferenceObject $Reference -DifferenceObject $Difference -IncludeEqual

[PsCustomObject]@{
    ONJ1 = ($compare | Where-Object {$_.SideIndicator -eq "<="}).InputObject -join [environment]::NewLine
    ONJ2 = ($compare | Where-Object {$_.SideIndicator -eq "=>"}).InputObject -join [environment]::NewLine
    Both = ($compare | Where-Object {$_.SideIndicator -eq "=="}).InputObject -join [environment]::NewLine
} | Format-Table -Wrap

Output:

ONJ1                                                      ONJ2                         Both                  
----                                                      ----                         ----                  
Lorem ipsum dolor sit amet,                               Lorem ipsum dolor sit amet,  sed do eiusmod tempor.
consectetur adipiscing elit,