Swift: loop over array elements and access previous and next elements

Question

In Swift, I want to loop over an array and compare each element to the previous and/or next. For each comparison I will either produce a new element or nothing. Is there \"funct

Answer 1

You can replace the while loop and i with a for loop and stride.

let a = [ 1,2,2,3,5,4,2,5,7,9,5,3,8,10 ]
var r: [Int] = []

for i in stride(from: 1, to: a.count - 1, by: 1) {
    if a[i] < a[i+1] && a[i] < a[i-1] {
        r.append(i)
    }
}

print(r)
// [6, 11]

You can get real fancy with a filter but this isn't nearly as readable as the above code:

let a = [ 1,2,2,3,5,4,2,5,7,9,5,3,8,10 ]
let r = a.enumerated().dropFirst().dropLast().filter { $0.1 < a[$0.0 + 1] && $0.1 < a[$0.0 - 1] }.map { $0.0 }
print(r)
// [6, 11]