multiMaps.Swift

extension SequenceType where Generator.Element: SequenceType {
  var transposeAndPad: [[Generator.Element.Generator.Element]]? {
    var genGen = self.generate()
    let first = genGen.next()
    var gens = AnySequence{genGen}.map{$0.generate()}
    return first.map { $0.map { leftEl in [leftEl] + gens.indices.map{gens[$0].next() ?? leftEl} }
    }
  }

  var transpose: [[Generator.Element.Generator.Element]] {
    var gens = self.map{$0.generate()}
    var ans: [[Generator.Element.Generator.Element]] = []
    for
      var toAp: [Generator.Element.Generator.Element] = [];;
      ans.append(toAp), toAp.removeAll(keepCapacity: true) {
      for ind in gens.indices {
        if let element = gens[ind].next() {
          toAp.append(element)
        } else {
          return ans
        }
      }
    }
  }
}

extension CollectionType where Generator.Element: CollectionType {
  var unsafeTranspose: [[Generator.Element.Generator.Element]] {
    return self.first!.indices.map{ ind in self.map{ $0[ind] } }
  }
}

extension SequenceType {
  func perMap
    <S: SequenceType, T where S.Generator.Element == (Generator.Element -> T)>
    (transforms: S) -> [[T]] {
      return self.map{element in transforms.map{$0(element)}}
    }
  func multiMap
    <S: SequenceType, T where S.Generator.Element == (Generator.Element -> T)>
    (transforms: S) -> [[T]] {
      return transforms.map{self.map($0)}
  }
}