Hash Tables

Hash tables (also called hashtables or dictionaries) are key-value pair collections in PowerShell, similar to associative arrays or dictionaries in other languages.

1. Creating Hash Tables

• Basic syntax:

  $hash = @{
    Name = 'Alice'
    Age = 30
    City = 'New York'
  }

• Empty hash table:

  $empty = @{}

• Ordered hash table (preserves insertion order):

  $ordered = [ordered]@{
    First = 1
    Second = 2
    Third = 3
  }

2. Accessing Values

$hash['Name']        # Alice
$hash.Name          # Alice (property syntax)
$hash.Age           # 30
$hash['NonExistent']  # Returns $null if key doesn't exist

3. Adding and Modifying

$hash['Email'] = 'alice@example.com'  # Add new key
$hash.Age = 31                        # Modify existing key
$hash.Add('Phone', '123-456-7890')    # Add using method

4. Removing Keys

$hash.Remove('City')    # Remove by key
$hash.Clear()           # Remove all keys

5. Checking Existence

$hash.ContainsKey('Name')    # True
$hash.ContainsValue('Alice') # True
'Name' -in $hash.Keys        # True

6. Iteration

# Iterate keys
foreach ($key in $hash.Keys) {
    "$key = $($hash[$key])"
}

# Iterate key-value pairs
$hash.GetEnumerator() | ForEach-Object {
    "$($_.Key) = $($_.Value)"
}

7. Converting to Objects

[pscustomobject]$hash    # Convert to custom object
$hash | ConvertTo-Json   # Convert to JSON

8. Nested Hash Tables

$nested = @{
    User = @{
        Name = 'Alice'
        Age = 30
    }
    Settings = @{
        Theme = 'Dark'
        Language = 'en'
    }
}
$nested.User.Name    # Alice

9. Common Use Cases

• Configuration storage
• Function parameters (splatting)
• Grouping data
• Lookup tables

10. Performance Notes

• Hash tables provide O(1) average lookup time
• For large datasets, consider using [System.Collections.Generic.Dictionary[K,V]] for better performance