Delete items in an array that are in another array

Question

I'm stuck with my script. I need to compare two arrays, one is the result of a query, the other one of a content of a file:

$Array1 = Invoke-Sqlcmd -Query "select name from person"

$Array2 = Get-Content ".\Myfile.txt" #the file is a set of one item
every line

Now, in $Array2 there are items that I would like to delete from the $Array1.

How can I do this? Thank you for yr help!

Answer 1

Use the Where-Object cmdlet to filter $Array1 based on what is in $Array2:

$Array1 = $Array1 |Where-Object { $Array2 -notcontains $_ }

That works if Invoke-Sqlcmd returns simple strings. If not, you could do something like:

$Array1 = $Array1 |Where-Object { $Array2 -notcontains $_.someProperty }

Answer 2

If performance is an issue, you can get faster results constructing an alternating regex from one of the arrays, and using it as an array operator against the other.

$Array1 = Invoke-Sqlcmd -Query "select name from person"

$Array2 = Get-Content ".\Myfile.txt" #the file is a set of one item
every line

$regex = ‘(?i)^(‘ + (($Array2 |foreach {[regex]::escape($_)}) –join “|”) + ‘)$’

$Array1 -notmatch $regex

Explanation of the code to build the regex here.