Question

我想了解在clojure中对不同大小的集合进行操作的惯用方法。有没有办法告诉函数'map'用一些默认值填充集合的其余部分？

举个例子，假设我有3个向量：

(def x [1 2 3 4])
(def y [1 2 3 4 5])
(def z [1 2 3 4 5 6 7])

(map + x y z)    ; yields (3 6 9 12)

在这种情况下，如何用零填充x和y并获得此收益：

(3 6 9 12 10 6 7)

Answer 1

map不会自行完成，但您可以使用concat和repeat的组合来获得所需的结果：

(def x [1 2 3 4])
(def y [1 2 3 4 5])
(def z [1 2 3 4 5 6 7])

(map +
     (concat x (repeat 0))
     (concat y (repeat 0))
     z) ; => (3 6 9 12 10 6 7)

以下是concat和repeat的API文档。

这里有一个草图，说明如何将它抽象出来，所以你不需要知道哪个集合最长。（在上面的代码段中，如果concat (repeat 0)所有集合都有(defn map-longest [f default & colls] (lazy-seq (when (some seq colls) (cons (apply f (map #(if (seq %) (first %) default) colls)) (apply map-longest f default (map rest colls)))))) (map-longest + 0 [1 2 3 4] [1 2 3 4 5] [1 2 3 4 5 6 7]) ; => (3 6 9 12 10 6 7)，那么您将拥有无限序列。

{{1}}

您可以看到其他几种方法作为this previous question on Stack Overflow的答案。

Answer 2

您可以通过以下功能合并长度可变的地图矢量：

  constructor(props)
  {

    super(props)

    this.state = {

      show: false,
      opticare: false
    }

    this.handleSwitch = this.handleSwitch.bind(this)
    this.leave = this.leave.bind(this)
    this.handleOpti = this.handleOpti.bind(this)
    this.handleCare = this.handleCare.bind(this)
  }

  handleSwitch = () => {
    this.setState({
      show: !this.state.switch

    })
  }
  leave = () => {

    this.setState({
      show: this.state.switch

    })

  }
  handleOpti = () => {
    this.setState({
      opticare: !this.state.opticare
    })
  }
  handleCare = () => {
    this.setState({
      opticare: this.state.opticare
    })
  }

  render()
  {
    let className = 'reading-friends'
    if (this.state.show) {
      className = 'reading-friends visible'
    } else if (!this.state.show) {
      className = 'reading-friends invisible'
    }

    let addClass = 'opti-care'
    if (this.state.opticare) {
      addClass = 'opti-care visible'
    } else if (!this.state.opticare) {
      addClass = 'opti-care invisible'
    }

    return (
      <div>
        <div>
          <div className="row ">
            <div className="row ">
              <div className={className} style={{ textAlign: 'center' }}>
                <h1 className="heading" style={{
                  fontSize: '50px',
                  fontWeight: 'bold',
                  marginTop: '140px',
                  marginBottom: '200px',
                  fontFamily: 'catamaran,sans-serif'
                }}>Reading Friends</h1>
                <p className="parah">Reading Friends is designed to engage young children by
                  promoting interactive learning through games, puzzles,<br/>
                  and music. Appealing to children's instinctual inquisitiveness,
                  Reading Friends brings education to life with exciting graphics,<br/>
                  spirited sound and creative activities
                  that help them learn to read, while entertaining them through play.</p>
              </div>
            </div>
          </div>
          <div className="row d-flex justify-content-center">
            <div style={{ textAlign: 'center' }} className={addClass}>
              <h1 style={{
                fontSize: '50px',
                fontWeight: 'bold',
                marginBottom: '200px',
                fontFamily: 'catamaran,sans-serif'
              }}>Opticare Solution</h1>
              <p>OptiCare Solution is a complete mini ERP for opticians and optometrists.<br/>
                We are the first to bring such an extensive solution in the field of Optometry,<br></br>
                providing features that are robust and easy to use.</p>
            </div>
          </div>
          <div className="row"></div>
        </div>
        <div style={{ marginTop: '270px' }} className="row ">

          <div className="col-lg-3 col-sm-3 col-3 d-flex justify-content-center">

            <a href="https://play.google.com/store/apps/details?id=com.planetreading.readingfriends">
              <img onMouseOut={this.leave} onMouseOver={this.handleSwitch}
                   src="http://newstate.io/wp-content/uploads/2019/07/work-reading-friends-colored.png"
                   alt="" class="we-do-img we-work-img img-responsive grayscale"/>
            </a>

          </div>
          <div className="col-lg-3 col-sm-3 col-3 d-flex justify-content-center">
            <img onMouseOut={this.handleCare} onMouseOver={this.handleOpti}
                 src="http://newstate.io/wp-content/uploads/2019/07/work-opticare-colored.png"
                 alt="" class="we-do-img we-work-img img-responsive grayscale"/>
          </div>
        </div>
      </div>
    )
  }

此功能使解决方案更加通用，可以采用任意长度的地图矢量。

在clojure中使用具有不同大小集合的“map”

2 个答案: