Compare Two CSVs, match the columns on 2 or more Columns, export specific columns from both csvs with powershell

Question

i Have 2 CSV\'s

left.csv

Ref_ID,First_Name,Last_Name,DOB
321364060,User1,Micah,11/01/1969
946497594,User2,Acker,05/28/1960
887327716,User3,Aco,06/26/1950         


        

Answer 1

Some good answers already, and here's another.

Import your myriad objects into a single (dis)array:

$left = @"
Ref_ID,First_Name,Last_Name,DOB
321364060,User1,Micah,11/01/1969
946497594,User2,Acker,05/28/1960
887327716,User3,Aco,06/26/1950
588496260,User4,John,05/23/1960
565465465,User5,Jack,07/08/2020
"@

$right = @"
First_Name,Last_Name,DOB,City,Document_Type,Filename
User1,Micah,11/01/1969,Parker,Transcript,T4IJZSYO.pdf
User2,Acker,05/28/1960,,Transcript,R4IKTRYN.pdf
User3,Aco,06/26/1950,,Transcript,R4IKTHMK.pdf
User4,John,05/23/1960,,Letter,R4IKTHSL.pdf
"@

$disarray = @(
    $left | ConvertFrom-Csv 
    $right | ConvertFrom-Csv
)

Use Group-Object to organize them into groups having identical key values:

$keyProps = @('First_Name', 'Last_name', 'DOB')
$disarray | 
    Group-Object -Property $keyProps | 
    Where-Object Count -gt 1 |

Then merge the objects, adding any missing properties to the output $mergedObject

    ForEach-Object {
        $mergedObject = $_.group[0]
        foreach ($obj in $_.group[1..($_.group.count-1)]) {
            $newProps = ($obj | Get-Member -MemberType NoteProperty).name | 
                Where-Object {
                    $_ -notin ($mergedobject | Get-Member -MemberType NoteProperty).name
                } 
            foreach ($propName in $newProps) {
                $mergedObject | Add-Member -MemberType NoteProperty -Name $propName -Value $obj.$propName -Force
            }
        }
        Write-Output $mergedObject
    }

This doesn't differ wildly from the answers you already have, but eliminating the "left" "right" distinction might be helpful; The above code should handle three or more sources thrown into $disarray, merging all objects containing identical $keyProps.

Note that there are corner cases to consider. For instance, what happens if one object has 'City=Chigago' for a user and another has 'City=New York'?