Parametrization of a pipe with a function - powershell

Question

I'm discovering powershell with some joy and some frustation, and I'm currently hitting a wall with respect to my powershell abilities.
I'd like to create a pipe function to summarize member types of a collection of objects.
Without a function, the working code looks like this:
get-process |
foreach { get-member -inputobject $_ } |
foreach { "[$($_.membertype)]$($_.name)" } |
group-object |
sort count, name
Now, my current attempt for a function achieving this is:
function get-membersummary {
process {
get-member -inputobject $_ |
foreach { "[$($_.membertype)]$($_.name)" } |
group-object |
sort count, name
}
}
it should be used like this:
&$anything | get-membersummary
The obvious problem is that the code in the "process" statement is called for each element, which means that the grouping is performed on each item. What I would like is the first result of the whole two lines to be subjected to the grouping.
Is it possible to achieve this in powershell without using an array variable that would induce memory inefficiency ?
Also, I'm pretty sure that this question as already been asked, but I couldn't find the correct words to express it.

Answer 1

You can use SteppablePipeline, but for sorting you have to collect whole input before start sorting it, so using array here hardly induce much more "memory inefficiency" than you already have.
function get-membersummary {
begin {
$Pipeline={
&foreach { get-member -inputobject $_ } |
foreach { "[$($_.membertype)]$($_.name)" } |
group-object|
sort count, name
}.GetSteppablePipeline()
$Pipeline.Begin($MyInvocation.ExpectingInput,$ExecutionContext)
}
process {
if($MyInvocation.ExpectingInput){
$Pipeline.Process($_)
}else{
$Pipeline.Process()
}
}
end {
$Pipeline.End()
$Pipeline.Dispose()
}
}

Answer 2

You can't group and sort until all data is received, so you need to wait until the end {} block in the function. Two examples:
#process using pipeline, but wait until end to group and sort
function get-membersummary {
begin { $res = #() }
process {
$res += Get-Member -inputobject $_ |
ForEach-Object { "[$($_.MemberType)]$($_.Name)" }
}
end {
$res | Group-Object | Sort-Object Count, Name | Select-Object Count, Name
}
}
#do everything after all objects have arrived
function get-membersummary2 {
end {
#in process { }, $input is the object in the pipeline. in end { } it is a collection of all the objects.
$input | % {
Get-Member -InputObject $_ |
ForEach-Object { "[$($_.MemberType)]$($_.Name)" }
} | Group-Object | Sort-Object Count, Name | Select-Object Count, Name
}
}
Get-Process | get-membersummary | ft -AutoSize
#Get-Process | get-membersummary2 | ft -AutoSize
Output:
Count Name
----- ----
75 [AliasProperty]Handles
75 [AliasProperty]Name
75 [AliasProperty]NPM
75 [AliasProperty]PM
75 [AliasProperty]VM
75 [AliasProperty]WS
75 [Event]Disposed
75 [Event]ErrorDataReceived
75 [Event]Exited
75 [Event]OutputDataReceived
....
On a general note, you should avoid using Group-Object and Sort-Object in functions as they break the flow of the pipeline. Select-Object (which I added this time) should also be avoided because it destroys the original objects. I understand the choice in this scenario, but be careful not the use them too much. You could have written a function or filter to process the objects, and then call group and sort manually when needed, like:
filter get-membersummary3 {
$_ |
Get-Member |
ForEach-Object { "[$($_.MemberType)]$($_.Name)" }
}
Get-Process | get-membersummary3 | Group-Object | Sort-Object Count, Name | Select-Object Count, Name