Compare 2 .csv files - powershell

Question

I have two .csv files with many information in it. If at the end of the sentence is a "M", I have to look if this row is in the other file. When it's there I have to look if the code at the beggining of the row is the same, when not then I have to do nothing, but when it's the same I have to make a new file.
This is the information I have to look if it's in the other file:
You can see that the information is here:
I also have rows with a "B" at the end but this is unimportant:
Now, when the information is here, I have to export all rows that are same in both files.
I have to export the rows in a new file which have the same code at the beginning which is circeld in red:
I have tried different solutions that I looked up in the Internet, but nothing really works.
Perhaps something like this?
$datenbank = Import-Csv "C:\Users\information1.csv"
$zentral = Import-Csv "C:\Users\information2.csv"
$new = ""
foreach ($line in $datenbank) {
$Spalte = $line.Split(",")
foreach ($z in $Zentral) {
$found = $false
foreach ($d in $Datenbanktyp) {
if ($d.$Spalte[1] -eq $z.$Spalte[1]) {
$found = $true
}
}
if ($found -eq $true) {
$new += $z
}
}
}
Or can it work with a if..elseif..else loop?

Answer 1

Let's see if I got this right. You have one file where the second-last column contains a letter. If that letter is "M" you want to check if the value of the column before that (partially) matches a column from a second file. If it does, you then want to export all rows from the second file that have the same value in the first column as the matched row to a new file.
Since you didn't reveal the column names I'm going to dub the third- and second-last columns from the first file "Erin" and "Marty", the match column from the second file "Pat", and the first column from the second file "Gene".
$datenbank | Where-Object {
$_.Marty -ceq 'M'
} | Select-Object -Expand Erin -Unique | ForEach-Object {
$outfile = "export_${_}.csv" # adjust output filename as you see fit
$firstcol = $zentral |
Where { $_.Pat -like "*${_}*" } |
Select-Object -Expand Gene
$zentral | Where-Object {
$_.Gene -eq $firstcol
} | Export-Csv $outfile
}
Another approach would be to group your second file by the first column and then check if the groups contain a matching value.
$groups = $zentral | Group-Object Gene
$datenbank | Where-Object {
$_.Marty -ceq 'M'
} | Select-Object -Expand Erin -Unique | ForEach-Object {
$outfile = "export_${_}.csv" # adjust output filename as you see fit
$groups | Where-Object {
$_.Group.Pat -like "*${_}*"
} | Select-Object -Expand Group | Export-Csv $outfile
}
Replace "Erin", "Marty", "Pat" and "Gene" with the actual column titles from your CSV files. Should your files not contain column titles you need to specify them via the -Header parameter of Import-Csv, otherwise the cmdlet will interpret the first data row as the headers.