Converting an indexPath to the correct index of a one dimension array

IndexPathToIndexConversion.swift

let originalArray = [1, 2, 3, 4, 5, 6]
let sections = [[1, 2, 3], [5, 6]]

let indexPath = IndexPath(section: 0, row: 1)

let sectionTotal = self.sections.prefix(upTo: indexPath.section).map { $0.count }.reduce(0, +)
let index = sectionTotal + indexPath.row
let element = originalArray[index]
// element is `2`