Hash Tables

A hash table stores key-value pairs — look up a value by its key instead of by position.

Real-world analogy: a contacts list: you find a number by the person's name, not by where it is in the list.

$ages = @{
  Ada   = 36
  Linus = 28
}

$ages['Ada']
$ages.Linus
$ages['Grace'] = 45
$ages.Count
$ages.ContainsKey('Linus')
$ages.Remove('Linus')
$ages.Keys | Sort-Object

36
28
3
True
Ada
Grace

• @{ key = value; ... } creates a hash table. Keys are case-insensitive.
• Read with $h['key'] or $h.key; assign to add or change.
• Keys come back in no particular order. Use [ordered]@{ ... } to keep insertion order.

Looping over a hash table

$stock = [ordered]@{ apples = 10; pears = 0; plums = 4 }

foreach ($item in $stock.GetEnumerator()) {
  '{0}: {1}' -f $item.Key, $item.Value
}

apples: 10
pears: 0
plums: 4

Counting with a hash table

$counts = @{}
foreach ($word in 'red', 'blue', 'red', 'green', 'red') {
  $counts[$word] += 1
}
$counts.GetEnumerator() | Sort-Object Value, Key -Descending | ForEach-Object { "$($_.Value) $($_.Key)" }

3 red
1 green
1 blue

A missing key returns $null, and $null + 1 is 1 — so += 1 works even the first time a word is seen.

Splatting

A hash table can pass parameters to a command — called splatting (note the @ instead of $):

$params = @{
  Year   = 2025
  Month  = 12
  Day    = 25
  Format = 'dddd'
}
Get-Date @params

Thursday

Splatting keeps long command lines readable, and lets you build up parameters conditionally before calling a command.