Adding columns and manipulating existing column values in csv file using powershell - powershell

Question

I have a lot of csv files with values arranged like so:
X1,Y1
X2,Y2
...,...
Xn,Yn
I find it very tedious processing these with excel, so I want to setup a batch script to process these files such that they appear like this:
#where N is a specified value like 65536
X1,N-Y1,1
X2,N-Y2,2
...,...,...
Xn,N-Yn,n
I have only recently started using powershell for image processing (really simple scripts) and file name appending, so I am not certain how to go about this. A lot of the scripts I have encountered looking to answer this question use csv files with titles per column whereas my files are just arrays of values without object titles in the first row. I would like to avoid running multiple scripts to add titles.
My bonus question is something I have yet to find a good answer to at all, and is the most tedious part of processing. Using excels sort function, I usually change the order of the Yn values in Col2 such that they are sorted in the exported csv like so:
X1,N-Yn,n
...,...,...
Xn-1,N-Y2,2
Xn,N-Y1,1
Using the Col3 values as the sorting order (largest to smallest), then I delete this column so that the final saved csv only contains the first two columns (crucial step). Any help at all would be greatly appreciated, I apologize for the long-winded-ness of this question.

Answer 1

I have encountered looking to answer this question use csv files with titles per column whereas my files are just arrays of values without object titles in the first row.
The -Header parameter of Import-Csv is for adding column headers when the file does not contain them. It takes an array of strings, of however many columns there are.
I would like to avoid running multiple scripts to add titles.
If you couldn't use -Header, you could read the lines with Get-Content into memory, add a header in memory, and then use ConvertFrom-CSV all in one script.
That said, if I'm reading it rightly, you want:
No headers in the input file, and I imagine no headers in the output file
The whole point of adding the third column and sorting and removing it is just to reverse the lines?
The only column you keep is column 1?
I wouldn't use Import-Csv for this, it won't make it much nicer.
$n = 65536
# Read lines into a list, and reverse it
$lines = [Collections.Generic.List[String]](Get-Content -LiteralPath 'c:\test\test.csv')
$lines.Reverse()
# Split each line into two, create a new line with X and N-Y
# write new lines to an output file
$lines | ForEach-Object {
$x, $y = $_.split(',')
"$x,$($n - [int]$y)"
} | Set-Content -LiteralPath 'c:\test\output.csv' -Encoding Ascii
If you do want to use CSV handling, then:
$n = 65536
$counter = 1
Import-Csv -LiteralPath 'C:\test\test.csv' -Header 'ColX', 'ColY' |
Add-Member -MemberType ScriptProperty -Name 'ColN-Y' -Value {$n - $_.ColY} -PassThru |
Add-Member -MemberType ScriptProperty -Name 'N' -Value {$script:counter++} -PassThru |
Sort-Object -Property 'N' -Descending |
Select-Object -Property 'ColX', 'ColN-Y' |
Export-Csv -LiteralPath 'c:\test\output.csv' -NoTypeInformation
But the output will have CSV headers and double-quoted values.

Answer 2

I would try something like, by extending the original table with a calculatable script-property as a new column:
#Your N number
$N = 65536
# Import CSV file without header columns
$table = Import-Csv -Header #("colX","colY") `
-Delimiter ',' `
-Path './numbers.csv'
Write-Host "Original table"
$table | Format-Table
# Manipulate table
$newtable = $table |
Add-Member -MemberType ScriptProperty -Name colNX -Value { $N-$this.colX } - PassThru
Write-Host "New table"
$newtable | Format-Table