Count unique numbers in CSV (PowerShell or Notepad++) - powershell

Question

How to find the count of unique numbers in a CSV file? When I use the following command in PowerShell ISE
1,2,3,4,2 | Sort-Object | Get-Unique
I can get the unique numbers but I'm not able to get this to work with CSV files. If for example I use
$A = Import-Csv C:\test.csv | Sort-Object | Get-Unique
$A.Count
it returns 0. I would like to count unique numbers for all the files in a given folder.
My data looks similar to this:
Col1,Col2,Col3,Col4
5,,7,4
0,,9,
3,,5,4
And the result should be 6 unique values (preferably written inside the same CSV file).
Or would it be easier to do it with Notepad++? So far I have found examples only on how to count the unique rows.

Answer 1

You can try the following (PSv3+):
PS> (Import-CSV C:\test.csv |
ForEach-Object { $_.psobject.properties.value -ne '' } |
Sort-Object -Unique).Count
6
The key is to extract all property (column) values from each input object (CSV row), which is what $_.psobject.properties.value does;
-ne '' filters out empty values.
Note that, given that Sort-Object has a -Unique switch, you don't need Get-Unique (you need Get-Unique only if your input already is sorted).
That said, if your CSV file is structured as simply as yours, you can speed up processing by reading it as a text file (PSv2+):
PS> (Get-Content C:\test.csv | Select-Object -Skip 1 |
ForEach-Object { $_ -split ',' -ne '' } |
Sort-Object -Unique).Count
6
Get-Content reads the CSV file as a line of strings.
Select-Object -Skip 1 skips the header line.
$_ -split ',' -ne '' splits each line into values by commas and weeds out empty values.
As for what you tried:
Import-CSV C:\test.csv | Sort-Object | Get-Unique:
Fundamentally, Sort-Object emits the input objects as a whole (just in sorted order), it doesn't extract property values, yet that is what you need.
Because no -Property argument is passed to Sort-Object to base the sorting on, it compares the custom objects that Import-Csv emits as a whole, by their .ToString() values, which happen to be empty[1]
, so they all compare the same, and in effect no sorting happens.
Similarly, Get-Unique also determines uniqueness by .ToString() here, so that, again, all objects are considered the same and only the very first one is output.
[1] This may be surprising, given that using a custom object in an expandable string does yield a value: compare $obj = [pscustomobject] #{ foo ='bar' }; $obj.ToString(); '---'; "$obj". This inconsistency is discussed in this GitHub issue.