Combining Group-Object and ForEach-Object?

Question

I'm developing a cmdlet called Merge-Xsd that can merge similar XML schemas. It takes a list of paths, loads the schemas, merges them, and produces an XMLDocument as output.

All schemas of a particular file name are considered "similar", and so what I'm doing is getting all of the child items in a particular directory structure, grouping them according to the file name, and then trying to pass them to my custom cmdlet.

Grouping them is easy:

$grouping = Get-ChildItem -Recurse -Filter *.xsd |
    Group-Object -Property Name -AsHashTable -AsString

However, processing them as part of the same pipeline is not. I've gotten as close as this:

$grouping.Keys |
    ForEach-Object { ($grouping[$_] |
        Select-Object -ExpandProperty FullName | Merge-Xsd).Save("C:\Out\$_") }

But what I'd really like to be able to do is use ForEach-Object directly after Group-Object to iterate over each group item, thus eliminating the need for the separate $grouping variable.

How can I use ForEach-Object to get the key/value pair while keeping each invocation of Merge-Xsd scoped to that particular key/value pair?

20150224 UPDATE:

The Merge-Xsd option set is extremely basic:

NAME
    Merge-Xsd

SYNTAX
    Merge-Xsd [-Path] <string[]>  [<CommonParameters>]

It is really just intended for throwing a bunch of files at it in one go and having them merged into a single output, which is an XmlDocument . (I modeled the output off of ConvertTo-Xml .)

Answer 1

I think you could just nest it like this:

Get-ChildItem -Recurse -Filter *.xsd |
    Group-Object -Property Name | 
        ForEach-Object { 
           ($_.Group.FullName | Merge-Xsd).Save("C:\Out\$($_.Name)")
        }

I don't have your cmdlet or files but in my limited testing this would work.

Some Explanation

I took out the -AsHash and -AsString parameters so we could deal directly with the group objects returned by Group-Object .

The $_.Group.FullName is more complex than it seems on first glance. $_ here refers to a single group object, since we're in a ForEach-Object . The group object contains a property called Name which is the name of the group, and a property called Group which is actually a collection of the the individual items within the group, so $_.Group is a collection.

From here, it would make sense to pipe that to ForEach-Object again, since each of the items in that collection will be a FileInfo object, and you want to get the FullName property to pass to Merge-Xsd .

Here we take advantage of some powershell magic. When you refer to $c.Property where $c is a collection of objects with a Property property, you get back a collection that consists of the property objects.

So $props = $c.Property is the same as:

$props = $c | ForEach-Object { $_.Property }

Knowing that, we can pipe $_.Group.FullName directly into Merge-Xsd to pass along all of the fullnames from all of the files in the group .

In that context, $_.Name still refers to the group object, so it's the name of the group, not the name of the file.