Unlike a list or a set, a map is a collection of entries. When using a map as a for loop iterator, we can iterate through each entry of the map or through just the keys, or just the values.

When iterating through a map, the loop variable will hold one entry per iteration. The entry’s key and value can be accessed using the properties, key and value:

val myClothes = mapOf("Shirts" to 7, "Pairs of Pants" to 4, "Jackets" to 2)

for (itemEntry in myClothes) {
  println("I have ${itemEntry.value} ${itemEntry.key}")
}

Notice that in order to access the attributes in a String template, we surround the loop variable and the attribute in curly brackets.

We can also access the key and value of each entry by destructuring using two loop variables in parentheses. The first variable is the entry’s key and the second is the value:

val myClothes = mapOf("Shirts" to 7, "Pairs of Pants" to 4, "Jackets" to 2)

for ((itemName, itemCount) in myClothes) {
  println("I have $itemCount $itemName")
}

Both examples have the same output:

I have 7 Shirts
I have 4 Pairs of Pants
I have 2 Jackets

Lastly, we can iterate through just a map’s keys or values. A map has the properties keys and values which can each be used as an iterator:

val myClothes = mapOf("Shirts" to 7, "Pairs of Pants" to 4, "Jackets" to 2)

println("KEYS")
for (itemName in myClothes.keys) {
  println(itemName)
}

println("\nVALUES")
for (itemCount in myClothes.values) {
  println(itemCount)
}

Here is the output:

KEYS
Shirts
Pairs of Pants
Jackets

VALUES
7
4
2