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\"] =          


        

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

As mentioned in a previous answer, clone is the way to go. I had a need to replace any null values in a hash with "Unknown" nd this one-liner does the job.

($record.Clone()).keys | %{if ($record.$_ -eq $null) {$record.$_ = "Unknown"}}

Answer 3

It seems when you update the hash table inside the foreach loop, the enumerator invalidates itself. I got around this by populating a new hash table:

$myHash = @{}
$myHash["a"] = 1
$myHash["b"] = 2
$myHash["c"] = 3

$newHash = @{}
foreach($key in $myHash.keys){
    $newHash[$key] = 5
}
$myHash = $newHash

Answer 4

You have to get creative!

$myHash = @{}
$myHash["a"] = 1
$myHash["b"] = 2
$myHash["c"] = 3

$keys = @()
[array] $keys = $myHash.keys

foreach($key in $keys)
{
    $myHash.Set_Item($key, 5)
}

$myHash

Name                         Value
----                         -----
c                              5
a                              5
b                              5

Answer 5

$myHash = @{
    Americas = 0;
    Asia = 0;
    Europe = 0;
}

$countries = @("Americas", "Asia", "Europe", "Americas", "Asia")

foreach($key in $($myHash.Keys))
{
    foreach($Country in $countries)
    {
        if($key -eq $Country)
        {
            $myHash[$key] += 1
        }
    }
}

$myHash

Answer 6

$myHash = @{
    Americas = 0;
    Asia = 0;
    Europe = 0;
}

$countries = @("Americas", "Asia", "Europe", "Americas", "Asia")

foreach($key in $($myHash.Keys))
{
    foreach($Country in $countries)
    {
        if($key -eq $Country)
        {
            $myHash[$key] += 1
        }
    }
}

Updating a hash value if array elements matched with a hash key.