Powershell hashtable with multiple values and one key

user_8672160 0
Viewed 31265

Im looking for a data structure/cmdlet that will allow me to add multiple values to a single key in Powershell.

My data would ideally look like this:

KEY-------------------------- VALUES

HOSTNAME1-------------DATABASE1,DATABASE2,DATABASE3

HOSTNAME2-------------DATABASE1,DATABASE2

etc...

I thought a hashtable would do the trick, but I'm unable to do the following:

$servObjects = @{}
$servObjects.Add("server1", @())
$servObjects.get_item("server1") += "database1"

This yields an empty array when I try:

$servObjects.get_item("server1")

I have also tried to do the following, hoping that powershell would understand what I want:

$servObjects2 = @{}
$servObjects2.add($servername, $databasename)

This will unfortunately yield a duplicate key exception

Thanks for any and all input

data-structures powershell
4 Answers

You basically want a hash table with values that are arrays. You don't have to use $hashtable.get_item or .add

$myHashTable = @{} # creates hash table
$myHashTable.Entry1 = @() #adds an array
$myHashTable.Entry1 += "element1"
$myHashTable.Entry1 += "element2"

This results in the following output:

$myHashTable

Name                           Value                                                                                                                                                                                           
----                           -----                                                                                                                                                                                           
Entry1                         {element1, element2}

$myHashTable.Entry1
element1
element2
user_61377090

In your original example, instead of writing

$servObjects.get_item("server1") += "database1"

you had written

$servObjects.server1 += "database1"

it would have worked.

I'm very new to PowerShell, but I prefer to use 

$servObjects.Add("key",@())

over

$servObjects.key = @())

because the .Add will throw a duplicate exception if the key is already present in the hashtable, whereas the assignment will replace an existing entry with a new one. For my purposes, I have found that the implicit replacement is (more often than not) an error, either in my logic, or an anomaly in the input data that needs to be handled.

user_30582780

If you have your data in an array you can group the array and convert to a hash table:

$ary = @()
$ary = $ary + [PSCustomObject]@{RowNumber = 1; EmployeeId = 1; Value = 1 }
$ary = $ary + [PSCustomObject]@{RowNumber = 2; EmployeeId = 1; Value = 2 }
$ary = $ary + [PSCustomObject]@{RowNumber = 3; EmployeeId = 2; Value = 3 }
$ary = $ary + [PSCustomObject]@{RowNumber = 4; EmployeeId = 2; Value = 4 }
$ary = $ary + [PSCustomObject]@{RowNumber = 5; EmployeeId = 3; Value = 5 }

$ht = $ary | Group-Object -Property EmployeeId -AsHashTable

$ht is then:

Name Value
---- -----
3    {@{RowNumber=5; EmployeeId=3; Value=5}}
2    {@{RowNumber=3; EmployeeId=2; Value=3}, @{RowNumber=4; EmployeeId=2; Value=4}}
1    {@{RowNumber=1; EmployeeId=1; Value=1}, @{RowNumber=2; EmployeeId=1; Value=2}}
user_6083970

If you know the value at creation time, it would be clearer this way :

[hashtable]$hash = @{
    HOSTNAME1 = @(DATABASE1, DATABASE2, DATABASE3);
    HOSTNAME2 = @(DATABASE1, DATABASE2);
}

Which will get you the following :

Name                           Value
----                           -----
HOSTNAME2                      {DATABASE1, DATABASE2}
HOSTNAME1                      {DATABASE1, DATABASE2, DATABASE3}
user_9716930
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