拆分大阵中的两个元素的数组 [英] Split large Array in Array of two elements

问题描述

我有对象的大名单，我需要他们一个组UI propouse两个元素的分裂。

I have large list of objects and I need to split them in a group of two elements for UI propouse.

例如：

[0，1，2，3，4，5，6]

变得与这四个数组的数组

Becomes an array with these four arrays

[[0，1]，[2，3]，[4，5]，[6]]

有一吨的方式来分割阵列。但是，什么是最有效的（成本最低）如果数组是巨大的。

There are a ton of ways to split an array. But, what is the most efficient (least costly) if the array is huge.

推荐答案

如果你正在寻找的效率，你可以有，将产生2个元素的每个阵列懒洋洋，所以你只存储在2个元素的方法时间在内存中：

If you're looking for efficiency, you could have a method that would generate each array of 2 elements lazily, so you'd only store 2 elements at a time in memory:

public struct ChunkGen<G : GeneratorType> : GeneratorType {

  private var g: G
  private let n: Int
  private var c: [G.Element]

  public mutating func next() -> [G.Element]? {
    var i = n
    return g.next().map {
      c = [$0]
      while --i > 0, let next = g.next() { c.append(next) }
      return c
    }
  }

  private init(g: G, n: Int) {
    self.g = g
    self.n = n
    self.c = []
    self.c.reserveCapacity(n)
  }
}

public struct ChunkSeq<S : SequenceType> : SequenceType {

  private let seq: S
  private let n: Int

  public func generate() -> ChunkGen<S.Generator> {
    return ChunkGen(g: seq.generate(), n: n)
  }
}

public extension SequenceType {
  func chunk(n: Int) -> ChunkSeq<Self> {
    return ChunkSeq(seq: self, n: n)
  }
}

var g = [1, 2, 3, 4, 5].chunk(2).generate()

g.next() // [1, 2]
g.next() // [3, 4]
g.next() // [5]
g.next() // nil

此方法适用于任何序列类型，而不仅仅是阵列。

This method works on any SequenceType, not just Arrays.

有关雨燕1，未经协议扩展，你有：

For Swift 1, without the protocol extension, you've got:

public struct ChunkGen<T> : GeneratorType {

  private var (st, en): (Int, Int)
  private let n: Int
  private let c: [T]

  public mutating func next() -> ArraySlice<T>? {
    (st, en) = (en, en + n)
    return st < c.endIndex ? c[st..<min(en, c.endIndex)] : nil
  }

  private init(c: [T], n: Int) {
    self.c = c
    self.n = n
    self.st = 0 - n
    self.en = 0
  }
}

public struct ChunkSeq<T> : SequenceType {

  private let c: [T]
  private let n: Int

  public func generate() -> ChunkGen<T> {
    return ChunkGen(c: c, n: n)
  }
}

func chunk<T>(ar: [T], #n: Int) -> ChunkSeq<T> {
  return ChunkSeq(c: ar, n: n)
}

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