groupBy

groupBy.swift

func groupBy<T>(equivalent:(a:T,b:T)->Bool, items:[T]) -> [[T]] {
  var lastItem:T? = nil
  var groups:[[T]] = []
  var currentGroup:[T] = []
  for item in items {
    if lastItem == nil {
     // first item
      currentGroup.append(item)
    }
    else {
      // same kind of item
      if equivalent(a: item,b: lastItem!) {
        currentGroup.append(item)
      }
      // new kind of item
      else {
        // tie off old item
        groups.append(currentGroup)
        currentGroup = []
        currentGroup.append(item)
      }
    }
    lastItem = item
  }
  // tie off last group
  groups.append(currentGroup)
  
  return groups
}