PowerShell By Example: Hashtables

In the arrays example we saw how to create arrays. In this example we will see how to create hashtables.

A hashtable is a data structure, similar like an array, but with a hashtable each value is stored with a key. You can compare it to a key/value store database structure.

To declare a hastable we use the @{} syntax:

$employees = @{}

This is different from the arrays where the @() is used.

Adding items to a hashtable

To add an item to a hashtable we use the Add method:

$employees = @{}

# Adding values using integers
$employees.Add(1, "John")
$employees.Add(2, "Mary")
$employees.Add(3, "Bob")
$employees.Add(4, "Sam")

$address = @{}

# Adding values using strings
$address.Add("John", "123 Main Street")
$address.Add("Mary", "456 North Street")
$address.Add("Bob", "789 West Street")
$address.Add("Sam", "321 South Street")

# Creating the hashtable in one go with values
$zipCodes = @{
    "John" = "12345"
    "Mary" = "54321"
    "Bob" = "98765"
    "Sam" = "32145"
}

Accessing items from a hashtable

To access an item from a hashtable you use the [key] syntax:

$employees[4]
$address["Mary"]
$zipCodes.Sam

Result:

Sam
456 North Street
32145

Notice that this looks similar like an array, but the key is used instead of the index. The key can be an integer or a string if you like. The example above also directly used the key to get the value in the hashtable.

Loop through a hashtable

Accessing a hashtable in a loop is similar to the example you saw before. There are several ways we can loop through a hashtable.

$employees.keys | Sort-Object $_ | ForEach-Object {
    Write-Host "Employee ID $($_) : $($employees[$_])"
}

foreach ($key in $address.Keys) {
    Write-Host "$($key) lives at $($address[$key])"
}

Result:

Employee ID 1 : John
Employee ID 2 : Mary
Employee ID 3 : Bob
Employee ID 4 : Sam

Bob lives at 789 West Street
Mary lives at 456 North Street
John lives at 123 Main Street
Sam lives at 321 South Street

Notice that we can use the keys method to get the keys of the hashtable and then use that particular value in the loops to get the value. The script also uses the Sort-Object command to sort the keys.

Hastable with different properties

Within a hashtable you are not bound to the key/value pair. You can create a hashtable with different properties.

$employeeAddress = @{
    Name    = "Mary"
    Address = "456 North Street"
    Zipcode = "54321"
}

$employeeAddress

Name                           Value
----                           -----
Name                           Mary
Zipcode                        54321
Address                        456 North Street

Removing properties from a hashtable

To remove a property from a hashtable you use the Remove method:

$employeeAddress = @{
    Name    = "Mary"
    Address = "456 North Street"
    Zipcode = "54321"
}

$employeeAddress.Remove("Zipcode")

$employeeAddress

Result:

Name                           Value
----                           -----
Name                           Mary
Address                        456 North Street

Sort a hashtable

There are various ways we can sort a hashtable.

The first thing we can do is create an ordered hashtable.

$addresses = @()

$addresses += [ordered]@{Name = "John"; Address = "123 Main Street" }
$addresses += [ordered]@{Name = "Sam"; Address = "321 South Street" }

$addresses += @{Name = "Mary"; Address = "456 North Street" }
$addresses += @{Name = "Bob"; Address = "789 West Street" }

$addresses

Result:

Name                           Value
----                           -----
Name                           John
Address                        123 Main Street
Name                           Sam
Address                        321 South Street
Name                           Mary
Address                        456 North Street
Name                           Bob
Address                        789 West Street

What happens here is that the first and last item keys are ordered differently. In the first two rows the Name and Address keys are displayed and for the next two rows the Address and Name keys are displayed. That is because it is possible to set the order in which the items need to be iterated through. Once the ordered keyword is used the items will be displayed in that order.

Another thing we can do is sort the hashtables by key:

$addresses = @()

$addresses += @{Name = "John"; Address = "123 Main Street" }
$addresses += @{
  Name = "Sam"
  Address = "321 South Street"
}
$addresses += @{Name = "Mary"; Address = "456 North Street" }
$addresses += @{Name = "Bob"; Address = "789 West Street" }

$addresses | Sort-Object -Property @{e = { $_.Name } }

Result:

Name                           Value
----                           -----
Address                        789 West Street
Name                           Bob
Address                        123 Main Street
Name                           John
Address                        456 North Street
Name                           Mary
Address                        321 South Street
Name                           Sam