Swift Dictionary Iteration
Dictionary iteration is visiting the entries of a dictionary one at a time. A loop can read each key and each value in turn.
Sorted keys, looked-up values
The loop walks the keys in sorted order. Each key prints beside its looked-up value.
let scores: [String: Int] = ["Ben": 75, "Ana": 90, "Cid": 60]
for key in scores.keys.sorted() {
print(key, scores[key] ?? 0)
}Summing every value
This loop visits each pair directly and adds its value. The final total does not depend on visit order.
let scores: [String: Int] = ["Ben": 75, "Ana": 90]
var total = 0
for pair in scores {
total += pair.value
}
print(total)Counting keys and values
Three entries give three keys and three values. Both counts print 3.
let scores: [String: Int] = ["Ana": 90, "Ben": 75, "Cid": 60]
print(scores.keys.count)
print(scores.values.count)Example
let prices: [String: Int] = ["pen": 3, "book": 12, "ruler": 5]
for key in prices.keys.sorted() {
print(key, prices[key] ?? 0)
}
var total = 0
for pair in prices {
total += pair.value
}
print(total)
print(prices.keys.count)Key points
- The keys view holds every key in a dictionary.
- Sorting the keys gives the loop a fixed, readable order.
- Each sorted key can look its own value back up.
- A direct loop over a dictionary hands over one key and value pair per turn.
- A total built inside a loop stays the same in any visit order.
- The keys count and the values count both match the entry count.
In this example, the first line builds a price dictionary with pen, book, and ruler. The sorted loop prints book with 12 first, then pen with 3, then ruler with 5. The second loop adds every value into a total. The next line prints that total, 20. The last line prints the key count, 3.
Note
A dictionary keeps no fixed order for its entries, so sorted keys are the safe route for printed lines.
Try it Yourself
Edit the code, then press Run.
Running is simulated · Programiz Swift Compiler
Exercise
Why does the sorted-keys loop print its lines in the same order on every run?