Friday Fun Convert Object to Hash Table

I've been working on a few PowerShell projects recently and one requirement I had was to turn an object into a hash table. I thought this was something that was already handled in PowerShell but I couldn't find a cmdlet or an easy .NET technique. So I wrote my own function, ConvertTo-Hashtable.

The function is designed to accept pipelined input and turns each object into an associative array, i.e., a hash table, and write the hash table to the pipeline.

Function ConvertTo-HashTable {

[cmdletbinding()]

Param(
[Parameter(Position=0,Mandatory=$True,HelpMessage="Please specify an object",
ValueFromPipeline=$True)]
[object]$InputObject,
[switch]$NoEmpty
)

Process {
Write-Verbose "Converting an object of type $($_.GetType().Name)"
#get propery names
$names=$InputObject | get-member -MemberType properties | select-object -expandproperty name
#define an empty hash table
$hash=@{}
#go through the list of names and add each property and value to the hash table
$names | foreach-object {
Write-Verbose "Adding property $_"
$hash.Add($_,$inputobject.$_)
} #foreach
if ($noEmpty) {
Write-Verbose "Parsing out empty values"
#define a new hash
$defined=@{}
#get items from $hash that have values and add to $defined
$hash.keys | foreach-object {
if ($hash.item($_)) {
$defined.add($_,$hash.item($_))
}
}
Write-Verbose "Writing the result to the pipeline"
Write-Output $defined
}
else {
Write-Verbose "Writing the result to the pipeline"
Write-Output $hash
} #If $noempty
}#close process
}#end function

As an object is processed by the function it uses Get-Member to retrieve all of the object's properties.

$names=$InputObject | get-member -MemberType properties | select-object -expandproperty name

The function then walks the object and adds each property name and value to a hash table.

#go through the list of names and add each property and value to the hash table
$names | foreach-object {
Write-Verbose "Adding property $_"
$hash.Add($_,$inputobject.$_)
} #foreach

This hash table object, $hash, eventually is written to the pipeline. This process happens to each piped in object. However, I also added a function parameter, -NoEmpty, to filter out properties with no values. When specified, the function creates a second hash table and then checks each key in $hash. If the corresponding item has a value, the key and value are added to the secondary hash.

if ($noEmpty) {
Write-Verbose "Parsing out empty values"
#define a new hash
$defined=@{}
#get items from $hash that have values and add to $defined
$hash.keys | foreach-object {
if ($hash.item($_)) {
$defined.add($_,$hash.item($_))
}
}
Write-Verbose "Writing the result to the pipeline"
Write-Output $defined

The secondary hash is then written to the pipeline. I had to take this approach because PowerShell doesn't like it when you try to modify and enumerate a hash table at the same time. Here's how you might use it:

PS S:\> $h=get-service spooler | convertto-hashtable
PS S:\> $h

Name Value
---- -----
ServiceName spooler
CanPauseAndContinue False
DisplayName Print Spooler
CanShutdown False
Site
Name spooler
MachineName .
ServiceType Win32OwnProcess, InteractiveProcess
Status Running
ServiceHandle SafeServiceHandle
Container
DependentServices {}
RequiredServices {HTTP, RPCSS}
ServicesDependedOn {HTTP, RPCSS}
CanStop True

Or to filter out the empty values:

PS S:\> get-service spooler | convertto-hashtable -NoEmpty

Name Value
---- -----
ServiceName spooler
DisplayName Print Spooler
RequiredServices {HTTP, RPCSS}
Name spooler
MachineName .
Status Running
ServiceHandle SafeServiceHandle
ServiceType Win32OwnProcess, InteractiveProcess
ServicesDependedOn {HTTP, RPCSS}
CanStop True

Granted, your use case for something like this is probably pretty limited. But there are some good technique examples here on working with hash tables.

The one nagging problem, at least until PowerShell v3, is that it is very difficult to write a sorted hash table. I'd love to write the hash table to the pipeline with sorted keys, but that may have to wait.

In the meantime, feel free to download and experiment with ConvertTo-Hashtable.

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