Optimizing lookups in PowerShell

Have you had a PowerShell script that contains two bigger arrays and you wanted merge the information. It can become quite slow if you need to search for every item from array A through all items in array B. The solution is called a HashTable! It might be not an advanced tip for some, but I was really glad to see a huge improvement, so I decided to share it as a post.

My Array A ($sites) is a list of SharePoint Sites (over 10K of them). For every site I need to get information on the owner (such as UsageLocation). In order to minimize calls to the server I want to reuse the information - in my array B: $users. This array of users has also thousands of entries.

Here is my main (simplified) setup:

Traversing the array B for the right item for every entry in array A is slow: Where-Object:

Using a hashtable is much faster:

In my example it took hours first. Now it takes seconds. A bonus: here is how you can convert an array to a hash table:

That’s all I’ve got today. Sharing is caring… And of course, big thanks to my colleague Anton H. for his advise.

• Array
• Filtering
• Hashtable
• Office 365
• Optimization
• PowerShell
• Sharepoint