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 could also iterate over indices and compare like this,

for i in a.indices.dropFirst().dropLast()
{
    if a[i] < a[a.index(after: i)],
            a[i] < a[a.index(before: i)] {
        r.append(i)
    }
}
print(r)
// [6, 11]

Or, something like this,

let result = a.indices.dropLast().dropFirst().filter { i in
    return a[i] < a[a.index(after: i)] &&
            a[i] < a[a.index(before: i)]
}
print(r)
// [6, 11]

Or, short,

let result = a.indices.dropLast()
                      .dropFirst()
                      .filter { a[$0] < a[$0 + 1] &&
                                a[$0] < a[$0 - 1] }
 print(result)