Group and Sum CSV with unknown number of columns - powershell

Question

Wondering if someone would be able to help me. Problem is that I'm trying to Import , Group, Sum and the Export a CSV. The problem is that my CSV has a unknown number of columns of the following format.
GroupA,GroupB,GroupC,ValueA,ValueB,ValueC,ValueD...
GroupA, B and C are constant and the fields I want to group by - I know the names of these fields in advance. The problem is there are an unknown number of Value columns - all of which I want to Sum (and don't know the names of in advance.)
I'm comfortable getting this code working if I know the name of the Value fields and have a fixed number of Value Fields. But I'm struggling to get code for unknown names and number of columns.
$csvImport = import-csv 'C:\input.csv'
$csvGrouped = $csvImport | Group-Object -property GroupA,GroupB,GroupC
$csvGroupedFinal = $csvGrouped | Select-Object #{Name = 'GroupA';Expression={$_.Values[0]}},
#{Name = 'GroupB';Expression={$_.Values[1]}},
#{Name = 'GroupC';Expression={$_.Values[2]}},
#{Name = 'ValueA' ;Expression={
($_.Group|Measure-Object 'ValueA' -Sum).Sum
}}
$csvGroupedFinal | Export-Csv 'C:\output.csv' -NoTypeInformation
Example Input Data -
GroupA, GroupB, Value A
Sam, Apple, 10
Sam, Apple, 20
Sam, Orange, 50
Ian, Apple, 15
Output Data -
GroupA, GroupB, Value A
Sam, Apple, 30
Sam, Orange, 50
Ian, Apple, 15

Answer 1

The following script should work. Pay your attention to the $FixedNames variable:
$csvImport = #"
Group A,Group B,Value A
sam,apple,10
sam,apple,20
sam,orange,50
ian,apple,15
"# | ConvertFrom-Csv
$FixedNames = #('Group A', 'Group B', 'Group C')
# $aux = ($csvImport|Get-Member -MemberType NoteProperty).Name ### sorted (wrong)
$aux = ($csvImport[0].psobject.Properties).Name ### not sorted
$auxGrpNames = #( $aux | Where-Object {$_ -in $FixedNames})
$auxValNames = #( $aux | Where-Object {$_ -notin $FixedNames})
$csvGrouped = $csvImport | Group-Object -property $auxGrpNames
$csvGroupedFinal = $csvGrouped |
ForEach-Object {
($_.Name.Replace(', ',','), (($_.Group |
Measure-Object -Property $auxValNames -Sum
).Sum -join ',')) -join ','
} | ConvertFrom-Csv -Header $aux
$csvGroupedFinal
Tested likewise for
$csvImport = #"
Group A,Group B,Value A,Value B
sam,apple,10,1
sam,apple,20,
sam,orange,50,5
ian,apple,15,51
"# | ConvertFrom-Csv
as well as for more complex data of Group A,Group B,Group C,Value A,Value B header.
Edit updated according to the beneficial LotPings' comment.

Answer 2

After importing this script splits the properties (columns) into Groups / Values
It groups dynamically and sums on only value fields independent of the number
The input ordering is maintained with a final Select-Object
## Q:\Test\2019\01\17\SO_54237887.ps1
$csvImport = Import-Csv '.\input.csv'
$Cols = ($csvImport[0].psobject.Properties).Name
# get list of group columns by name and wildcard
$GroupCols = $Cols | Where-Object {$_ -like 'Group*'}
# a different approach would be to select a number of leading columns
# $GroupCols = $Cols[0..1]
$ValueCols = $Cols | Where-Object {$_ -notin $GroupCols}
$OutCols = ,'Groups' + $ValueCols
$csvGrouped = $csvImport | Group-Object $GroupCols | ForEach-Object{
$Props = #{Groups=$_.Name}
ForEach ($ValCol in $ValueCols){
$Props.Add($ValCol,($_.Group|Measure-Object $ValCol -Sum).Sum)
}
[PSCustomObject]$Props
}
$csvGrouped | Select-Object $OutCols
With this sample input file
GroupA GroupB ValueA ValueB
------ ------ ------ ------
Sam Apple 10 15
Sam Apple 20 25
Sam Orange 50 75
Ian Apple 15 20
Sample output for any number of Groups and values
Groups ValueA ValueB
------ ------ ------
Sam, Apple 30 40
Sam, Orange 50 75
Ian, Apple 15 20
Without any change in code it does process data from Hassans answer too:
Groups ValueA ValueB ValueC
------ ------ ------ ------
Sam, Apple 30 4 20
Sam, Orange 50 4 5
Ian, Apple 15 3 3

Answer 3

script1.ps1
Import-Csv 'input.csv' | `
Group-Object -Property GroupA,GroupB | `
% {$b=$_.name -split ', ';$c=($_.group | `
Measure-Object -Property Value* -Sum).Sum;
[PScustomobject]#{GroupA=$b[0];
GroupB=$b[1];
Sum=($c | Measure-Object -Sum).Sum }}
input.csv
GroupA, GroupB, ValueA, ValueB, ValueC
Sam, Apple, 10, 1, 10
Sam, Apple, 20, 3, 10
Sam, Orange, 50, 4, 5
Ian, Apple, 15, 3, 3
OUTPUT
PS D:\coding> .\script1.ps1
GroupA GroupB Sum
------ ------ ---
Sam Apple 54
Sam Orange 59
Ian Apple 21