Compare .csv and add only rows with updated values - powershell

Question

I have 2 .csv files, they have matching columns, I am trying to compare the two and have a final output .csv that only has the differences
corpold.csv is a previous imported file.
corpnew.csv is the new import file.
I need to export a CSV that includes all items that are not in corpold.csv, only changed items that exist in both CSVs and exclude any rows that exist in corpold.csv but not in corpnew.csv.
$reference = Import-Csv -Path D:\corpold.csv
$lookup = $reference | Group-Object -AsHashTable -AsString -Property EMPID
$results = Import-Csv -Path D:\corpnew.csv | foreach {
$email = $_.EMAIL_ADDRESS
$status = $_.ACTIVE
$fs = $_.FIRST_NAME
$ls = $_.LAST_NAME
$id = $_.EMPID
$title = $_.JOB_TITLE
$code = $_.JOB_CODE
$type = $_.USER_TYPE
$designee = $_.DESIGNEE
$stores = $_.STORES
$hiredate = $_.HIRE_DATE
$dept = $_.DEPARTMENT
$grp = $_.GROUP
if ($lookup.ContainsKey($id)) {
# if exists in yesterdays file
# trying to figure out how to compare and only provide results into
# the Export-Csv that have changed while excluding any items in
# corpold that do not exist in corpnew
} else {
# if it does not exist update all fields
[PSCustomObject]#{
ACTIVE = $status
EMAIL_ADDRESS = $email
FIRST_NAME = $fs
LAST_NAME = $ls
EMPID = $id
JOB_TITLE = $title
JOB_CODE = $code
USER_TYPE = $type
DESIGNEE = $designee
STORES = $stores
HIRE_DATE = $hiredate
DEPARTMENT = $dept
GROUP = $grp
}
}
}
# Sample outputs
$results
$results | Export-Csv -Path D:\delta.csv -NoTypeInformation

Answer 1

There are two operations to be done here: find differences and compare objects which exist in both files.
Compare objects and find new/deleted entries
To compare object you can utilize Compare-Object cmdlet like this:
Compare-Object -ReferenceObject $reference -DifferenceObject $results -Property EMPID -IncludeEqual
This will give you the list of EMPID and SideIndicator showing whether object exist only in first (<=), only in second (=>) or in both (==). You can filter by SideIndicatorand then process it accordingly.
Alternative way is to use Where-Object like this:
$reference | Where-Object empid -NotIn $results.empid
$reference | Where-Object empid -In $results.empid
$results | Where-Object empid -NotIn $reference.empid
First one will give you entries only in first file, second one results existing in both, last one will give you entries only existing in second file.
Find edited entries
What you basically have to do is to iterate all the entries and then check if any of the columns has been changed. If yes, add it to $changedEntries.
Example of script:
$IDsInBoth = $results | Where-Object empid -In $reference.empid | Select-Object -ExpandProperty EMPID
$AllProperties = $results | Get-Member | Where-Object MemberType -eq "NoteProperty" | Select-Object -ExpandProperty Name
$changedEntries = #()
$IDsInBoth | ForEach-Object {
$changed = $false
$newEntry = $results | Where-Object EMPID -eq $_
$oldEntry = $reference | Where-Object EMPID -eq $_
foreach ($p in $AllProperties) {
if ($oldEntry."$p" -ne $newEntry."$p") {
$changed = $true
}
}
if ($changed) {
$changedEntries += $newEntry
}
}