PowerShell - Convert Property Names from Pascal Case to Upper Case With Underscores - powershell

Question

Let's say I have an object like this:
$test = #{
ThisIsTheFirstColumn = "ValueInFirstColumn";
ThisIsTheSecondColumn = "ValueInSecondColumn"
}
and I want to end up with:
$test = #{
THIS_IS_THE_FIRST_COLUMN = "ValueInFirstColumn";
THIS_IS_THE_SECOND_COLUMN = "ValueInSecondColumn"
}
without manually coding the new column names.
This shows me the values I want:
$test.PsObject.Properties | where-object { $_.Name -eq "Keys" } | select -expand value | foreach{ ($_.substring(0,1).toupper() + $_.substring(1) -creplace '[^\p{Ll}\s]', '_$&').Trim("_").ToUpper()} | Out-Host
which results in:
THIS_IS_THE_FIRST_COLUMN
THIS_IS_THE_SECOND_COLUMN
but now I can't seem to figure out how to assign these new values back to the object.

Answer 1

You can modify hashtable $test in place as follows:
foreach($key in #($test.Keys)) { # !! #(...) is required - see below.
$value = $test[$key] # save value
$test.Remove($key) # remove old entry
# Recreate the entry with the transformed name.
$test[($key -creplace '(?<!^)\p{Lu}', '_$&').ToUpper()] = $value
}
#($test.Keys) creates an array from the existing hashtable keys; #(...) ensures that the key collection is copied to a static array, because using the .Keys property directly in a loop that modifies the same hashtable would break.
The loop body saves the value for the input key at hand and then removes the entry under its old name.[1]
The entry is then recreated under its new key name using the desired name transformation:
$key -creplace '(?<!^)\p{Lu} matches every uppercase letter (\p{Lu}) in a given key, except at the start of the string ((?<!^)), and replaces it with _ followed by that letter (_$&); converting the result to uppercase (.ToUpper()) yields the desired name.
[1] Removing the old entry before adding the renamed one avoids problems with single-word names such as Simplest, whose transformed name, SIMPLEST, is considered the same name due to the case-insensitivity of hasthables in PowerShell. Thus, assigning a value to entry SIMPLEST while entry Simplest still exists actually targets the existing entry, and the subsequent $test.Remove($key) would then simply remove that entry, without having added a new one.
Tip of the hat to JosefZ for pointing out the problem.

Answer 2

I wonder if it is possible to do it in place on the original object?
($test.PsObject.Properties|Where-Object {$_.Name -eq "Keys"}).IsSettable says False. Hence, you need do it in two steps as follows:
$test = #{
ThisIsTheFirstColumn = "ValueInFirstColumn";
ThisIsTheSecondColumn = "ValueInSecondColumn"
}
$auxarr = $test.PsObject.Properties |
Where-Object { $_.Name -eq "Keys" } |
select -ExpandProperty value
$auxarr | ForEach-Object {
$aux = ($_.substring(0,1).toupper() +
$_.substring(1) -creplace '[^\p{Ll}\s]', '_$&').Trim("_").ToUpper()
$test.ADD( $aux, $test.$_)
$test.Remove( $_)
}
$test
Two-step approach is necessary as an attempt to perform REMOVE and ADD methods in the only pipeline leads to the following error:
select : Collection was modified; enumeration operation may not execute.
Edit. Unfortunately, the above solution would fail in case of an one-word Pascal Case key, e.g. for Simplest = "ValueInSimplest". Here's the improved script:
$test = #{
ThisIsTheFirstColumn = "ValueInFirstColumn";
ThisIsTheSecondColumn = "ValueInSecondColumn"
Simplest = "ValueInSimplest" # the simplest (one word) PascalCase
}
$auxarr = $test.PsObject.Properties |
Where-Object { $_.Name -eq "Keys" } |
select -ExpandProperty value
$auxarr | ForEach-Object {
$aux = ($_.substring(0,1).toupper() +
$_.substring(1) -creplace '[^\p{Ll}\s]', '_$&').Trim("_").ToUpper()
$newvalue = $test.$_
$test.Remove( $_)
$test.Add( $aux, $newvalue)
}
$test

Answer 3

This seems to work. I ended up putting stuff in a new hashtable, though.
$test = #{
ThisIsTheFirstColumn = "ValueInFirstColumn";
ThisIsTheSecondColumn = "ValueInSecondColumn"
}
$test2=#{}
$test.PsObject.Properties |
where-object { $_.Name -eq "Keys" } |
select -expand value | foreach{ $originalPropertyName=$_
$prop=($_.substring(0,1).toupper() + $_.substring(1) -creplace '[^\p{Ll}\s]', '_$&').Trim("_").ToUpper()
$test2.Add($prop,$test[$originalPropertyName])
}
$test2