5 ways to select Unique items in PowerShell 

Another method is to use Group-Object

“$set | select -unique” with the above sample gave an average result of 0.0732245000000091.

“Group $set” gave an average of 0.0612960800000009

This starts adding up when comparing multiple fields.

For a sample of 19456 records and selecting two unique fields from the set, “$set | Group A,B” (while adding the output to a result array) took only 34367.7835ms.

“$set | select -unique A,B” took 165405.4153ms – nearly 5x longer.

As a note for anyone who wants to use the Group method for multiple fields, an array of unique group objects is created for each result. Inside each object, any duplicate values are contained in the Group property. This means that capturing the first value from each Group property is unique for the combination of fields.

I have a set where the A field is a user name and the B field is an IP address. I group my $set into a new array by IP, then UserName – “$grp = $set | Group B,A”

The first result appears as below:
$grp[0] | ConvertTo-Json
{
“Values”: [
“10.180.9.40”
],
“Count”: 4,
“Group”: [
{
“A”: “MYDOMAIN\\MyApp”,
“B”: “10.180.9.40”
},
{
“A”: “MYDOMAIN\\MyApp”,
“B”: “10.180.9.40”
}
],
“Name”: “10.180.9.40”
}

The next item in the result array has the same account logging on from a different IP – there were 4 logons in total from the account
$grp[1] | ConvertTo-Json
{
“Values”: [
“10.180.9.41”
],
“Count”: 4,
“Group”: [
{
“User”: “MYDOMAIN\\MyApp”,
“IP”: “10.180.9.41”
},
{
“User”: “MYDOMAIN\\MyApp”,
“IP”: “10.180.9.41”
}
],
“Name”: “10.180.9.41”
}

To select Item 0 from each of the Group properties, we create another array and dump the unique results into that

$results = @()
$grp | foreach { $results += $_.group[0] }

The final result looks like this and is still quicker than the -select Unique method:

$results |ft -AutoSize

IP User
— —-
10.180.9.40 MYDOMAIN\\MyApp
10.180.9.41 MYDOMAIN\\MyApp