1

If I have a list of objects

$o1 = New-Object –TypeName PSObject –Property @{"MyKey"= "dog"; "MyValue"="Steve"}
$o2 = New-Object –TypeName PSObject –Property @{"MyKey"= "dog"; "MyValue"="Frank"}
$o3 = New-Object –TypeName PSObject –Property @{"MyKey"= "fish"; "MyValue"="Frank"}

$inputs = ($o1, $o2, $o3)

And a function that groups them into a table and then displays them

Function Report
{
    param($records)
    $hashtable = $records | Group-object -AsHashTable -Property "MyKey" 
    Write-host "Format table:"
    $hashtable | format-table
    Write-host "Contains key:"
    $hashtable.Keys | %{ "Key '$_' found: " + $hashtable.ContainsKey($_) }
}

So when I run this over my input list

Report($inputs)

I get

Name                           Value                                                                                                                             
----                           -----                                                                                                                             
dog                            {@{MyKey=dog; MyValue=Steve}, @{MyKey=dog; MyValue=Frank}}                                                                        
fish                           {@{MyKey=fish; MyValue=Frank}}                                                                                                    


Contains key:
Key 'dog' found: True
Key 'fish' found: True

As I would expect.

I can now run my list through select-object 

Report($inputs | select-object -Property MyKey, MyValue )

and get the same output from Report as above.

However if I use an expression for the MyKey value:

Report( $inputs | select-object -Property `
    @{ Label = "MyKey"; Expression = {$_.MyKey} },
    MyValue )

I get a grouped table that looks the same, but doesn't allow me to access values by key:

Name                           Value                                                                                                                             
----                           -----                                                                                                                             
dog                            {@{MyKey=dog; MyValue=Steve}, @{MyKey=dog; MyValue=Frank}}                                                                        
fish                           {@{MyKey=fish; MyValue=Frank}}                                                                                                    


Contains key:
Key 'dog' found: False
Key 'fish' found: False

Why can't I access this hashtable by key?

Note that this question looks a lot like this one but that solution did not work here. That is:

Add-Type -TypeDefinition @'
    public static class Helper {
        public static object IndexHashtableByPSObject(System.Collections.IDictionary table,object[] key) {
            return table[key[0]];
        }
    }
'@

Function Report
{
    param($records)
    $hashtable = $records | Group-object -AsHashTable -Property "MyKey" 
    $hashtable.Keys | %{ "Get using helper:" + [Helper]::IndexHashtableByPSObject($hashtable,$_) }
    $hashtable.Keys | %{ "Get using reflection:" + [Collections.IDictionary].InvokeMember('','GetProperty',$null,$hashtable,$_) }
}

returns

Get using helper:
Get using helper:
Get using reflection:
Get using reflection:

am I implementing those solutions wrong?

jdpilgrim
  • 358
  • 3
  • 13
  • Note that in my case, as an "alternative approach", I replaced `select-object` with `new-object` and that all worked fine. – jdpilgrim Sep 13 '17 at 10:45
  • Possible duplicate of [Group-Object diffencies with or without code block](https://stackoverflow.com/questions/28190053/group-object-diffencies-with-or-without-code-block) – user4003407 Sep 13 '17 at 17:06
  • Thanks @PetSerAl, that does _look_ very similar, but the solutions (helper, reflection) did not work for me. Could you give it a go with my example? – jdpilgrim Sep 27 '17 at 07:14
  • Two problems with your try: you should wrap `$_` into single element array, default to string conversion yield not very good result for your case: `$hashtable.Keys | %{ "Get using helper:" + (([Helper]::IndexHashtableByPSObject($hashtable,(,$_)) | % MyValue) -join ', ') }`. – user4003407 Sep 27 '17 at 09:32

0 Answers0