Enumerate String from specific index in nested loop in Swift

Question

To get characters from String using enumerated() method

let str = "Hello"

for (i,val) in str.enumerated() {
        print("\(i) -> \(val)")
}

now trying to enumerate same string inside for loop but from i position like

for (i,val) in str.enumerated() {
        print("\(i) -> \(val)")
        for (j,val2) in str.enumerated() {
            // val2 should be from i postion instead starting from zero
        }
}

How to enumerate and set j position should start from i?

Thanks

Answer 1

You can use dropFirst() to create a view in the string starting with a specific position:

for (i,val) in str.enumerated() {
    print("i: \(i) -> \(val)")
    for (j, val2) in str.dropFirst(i).enumerated() {
        print("j: \(i+j) -> \(val2)")
    }
}

You need to add i in the second loop if you want to get the index corresponding to the original string, otherwise j will hold the index in the view created by dropFirst()

Answer 2

You can use for in the str.indices and start inside loop based on outside loop.

let str = "abc"

for i in str.indices {
    for j in str[i...].indices {
        print(str[j])
    }
}

Output: a b c b c c

---

(Suggestion from @LeoDabus)

Answer 3

If I understood the problem statement correctly, the OP requires this -

Hello
ello
llo
lo
o

We can use the suffix method provided by Apple.

let str = "Hello"
var lengthOfString = str.count

for (i, val) in str.enumerated() {
    print(String(str.suffix(lengthOfString - i)))
}

We don't need the val in the for loop above, so we can rewrite the above for loop as below.

var str = "Hello"
var lengthOfString = str.count

for i in 0..<lengthOfString {
    print(String(str.suffix(lengthOfString - i)))
}

Both the above for loops will give the same desired output.