Brian Kernighan, in a lecture at the University of Nottingham, described a problem on which this task is based.

Problem

You are given a a data file of thousands of lines; each of three `whitespace` separated fields: a date, a one word name and the magnitude of the event.

Example lines from the file would be lines like:

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6
3/13/2009    CostaRica           5.1
Task

 Create a program or script invocation to find all the events with magnitude greater than 6
 Assuming an appropriate name e.g. "data.txt" for the file:
 Either: Show how your program is invoked to process a data file of that name.
 Or: Incorporate the file name into the program, (as it is assumed that the program is single use).


import Foundation
 
guard let path = Array(CommandLine.arguments.dropFirst()).first else {
  fatalError()
}
 
let fileData = FileManager.default.contents(atPath: path)!
let eventData = String(data: fileData, encoding: .utf8)!
 
for line in eventData.components(separatedBy: "\n") {
  guard let lastSpace = line.lastIndex(of: " "), // Get index of last space
        line.index(after: lastSpace) != line.endIndex, // make sure the last space isn't the end of the line
        let magnitude = Double(String(line[line.index(after: lastSpace)])),
        magnitude > 6 else { // Finally check the magnitude
    continue
  }
 
  print(line)
}