Question

How does one access data imported from a CSV file by using dynamic note property names? That is, one doesn’t know the colunm names beforehand. They do match a pattern and are extracted from the CSV file when the script runs.

As for an example, consider a CSV file:

"Header 1","Header A","Header 3","Header B"
0,0,0,0
1,2,3,4
5,6,7,8

I’d like to extract only columns that end with a letter. To do this, I read the header row and extract names with a regex like so,

$reader = new-object IO.StreamReader("C:\tmp\data.csv")
$line = $reader.ReadLine()
$headers = @()

$line.Split(",") | % {
    $m = [regex]::match($_, '("Header [A-Z]")')
    if($m.Success) { $headers += $m.value } }

This will get all the column names I care about:

"Header A"
"Header B"

Now, to access a CSV file I import it like so,

$csvData = import-csv "C:\tmp\data.csv"

Import-CSV will create a custom object that has properties as per the header row. One can access the fields by NoteProperty names like so,

$csvData | % { $_."Header A" } # Works fine

This obviously requires one to know the column name in advance. I’d like to use colunn names I extracted and stored into the $headers. How would I do that?

Some things I’ve tried so far

$csvData | % { $_.$headers[0] } # Error: Cannot index into a null array.
$csvData | % { $np = $headers[0]; $_.$np } # Doesn't print anything.
$csvData | % { $_.$($headers[0]) } # Doesn't print anything.

I could change the script like so it will write another a script that does know the column names. Is that my only solution?

Answer 1

the first thing ( and the only one… sorry) that came in my mind is:

$csvData | % { $_.$(( $csvData | gm | ? { $_.membertype -eq "noteproperty"} )[0].name) }

for get the first’s column values and

$csvData | % { $_.$(( $csvData | gm | ? { $_.membertype -eq "noteproperty"} )[1].name) }

for second column and so on….

is this what you need?