Powershell fastest way to merge two arrays using a common property? - performance

Question

What's the fastest way to merge two arrays using a common property?
Users | Select *
Username : Joe.Doe
Office : Chicago
Email :
Username : Mike.Smith
Office : New York
Email :
...
UserEmails | Select *
AccountEmail : Mike.Smith
EmailAddress : mike-smith#example.com
AccountEmail : Joe.Doe
EmailAddress : jsmith12#example.com
...
The merge should result in:
UsersCompleteList | Select *
Username : Joe.Doe
Office : Chicago
Email : jsmith12#example.com
Username : Mike.Smith
Office : New York
Email : mike-smith#example.com
...
Something like for each ($user in $users) { ($user.Email = $userEmails | ? { $_.AccountEmail -eq $user.Username}).EmailAddress takes ages on large datasets.

Answer 1

Loop through one collection and store the values in a hash. Then loop through the other collection and pull the value back out of the hash. Something like:
$hash = #{}
$userEmails | %{ $hash[$_.AccountEmail] = $_.EmailAddress }
$users | %{ $_.Email = $hash[$_.Username] }
If you have other properties you can just store the original object:
$hash = #{}
$userEmails | %{ $hash[$_.AccountEmail] = $_ }
$users | %{
$item = $hash[$_.Username]
$_.Email = $item.EmailAddress
$_.Other = $item.SomethingElse
}
Or with loops instead of ForEach-Object including:
$hash = #{}
foreach($e in $userEmails) {
$hash[$e.AccountEmail] = $e
}
foreach($u in $users) {
$item = $hash[$u.UserName]
if ($item -ne $null) {
$u.Email = $item.EmailAddress
}
}