Updating hash table values in a 'foreach' loop in PowerShell

Question

I'm trying to loop through a hash table and set the value of each key to 5 and PowerShell gives an error:

$myHash = @{} $myHash["a"] = 1 $myHash["b"] = 2 $myHash["c"] = 3  foreach($key in $myHash.keys){     $myHash[$key] = 5 } 

An error occurred while enumerating through a collection:

Collection was modified; enumeration operation may not execute.. At line:1 char:8 + foreach <<<< ($key in $myHash.keys){     + CategoryInfo          : InvalidOperation: (System.Collecti...tableEnumer    ator:HashtableEnumerator) [], RuntimeException     + FullyQualifiedErrorId : BadEnumeration 

What gives and how do I resolve this problem?

Answer 1

You can't modify Hashtable while enumerating it. This is what you can do:

$myHash = @{} $myHash["a"] = 1 $myHash["b"] = 2 $myHash["c"] = 3  $myHash = $myHash.keys | foreach{$r=@{}}{$r[$_] = 5}{$r} 

Edit 1

Is this any simpler for you:

$myHash = @{} $myHash["a"] = 1 $myHash["b"] = 2 $myHash["c"] = 3  foreach($key in $($myHash.keys)){     $myHash[$key] = 5 } 

Answer 2

There is a much simpler way of achieving this. You cannot change the value of a hashtable while enumerating it because of the fact that it's a reference type variable. It's exactly the same story in .NET.

Use the following syntax to get around it. We are converting the keys collection into a basic array using the @() notation. We make a copy of the keys collection, and reference that array instead which means we can now edit the hashtable.

$myHash = @{} $myHash["a"] = 1 $myHash["b"] = 2 $myHash["c"] = 3  foreach($key in @($myHash.keys)){     $myHash[$key] = 5 }