迭代关联数组的前 x 个元素

Question

具有 12 个元素的关联数组；

 this.rolls = {1:[], 2:[], 3:[], 4:[], 5:[],
                6:[], 7:[], 8:[], 9:[],10:[], 11:[], 12:[]};

获取前 10 个元素之和的最有效方法是什么。下面的代码目前对所有元素求和；

  var sum = 0;
  for (var k in this.rolls) {
    vals = this.rolls[k];
    for (var i=0; i<vals.length; i++) {
      sum += vals[i] || 0
    };
  };
  this.score = sum

前 10 个元素是：

 this.rolls = {1:[], 2:[], 3:[], 4:[], 5:[],
                    6:[], 7:[], 8:[], 9:[],10:[]};

这里是完整的代码：

function Game() {
  this.score = 0;
  this.frameOver = false;
  this.rolls = {1:[], 2:[], 3:[], 4:[], 5:[],
                6:[], 7:[], 8:[], 9:[],10:[], 11:[], 12:[]};
  this.currentFrame = 1;
  // this.lastFrameStrike = false;
  // this.lastFrameSpare = false;
  // this.isStrike = false
};

Game.prototype.roll = function(pins) {
  this.strikeOrSpare(pins);
  this.bonusDistributor(pins);
  this.rolls[this.currentFrame].push(pins);
  this.scoreUpdater(pins);
  this.frameHandler(pins);
  this.nextFrameBonus(pins)
};

// --------------------------------------------------

Game.prototype.strikeOrSpare = function(pins) {
  if (pins === 10) {
    this.isStrike = true;
    this.frameOver = true
  }
  else if (this.rolls[this.currentFrame][0] + pins === 10) {
    this.isSpare = true;
    this.frameOver = true
  };
};

// --------------------------------------------------

Game.prototype.bonusDistributor = function(pins) {
  if(this.wasSpare) { this.addToLastSpare(pins) };
  if(this.wasStrike) { this.addToLast(pins) };
  if(this.wasStrike2 && this.currentFrame > 1) { this.addToLastAgain(pins) };
};

// --------------------------------------------------

Game.prototype.addToLast = function(pins) {
  this.rolls[this.currentFrame - 1][0] += pins
};

Game.prototype.addToLastAgain = function(pins) {
  this.rolls[this.currentFrame - 2][0] += pins
};

Game.prototype.addToLastSpare = function(pins) {
  this.rolls[this.currentFrame - 1][1] += pins;
  this.wasSpare = false
};

// --------------------------------------------------

Game.prototype.scoreUpdater = function(pins) {
  var sum = Object.keys(this.rolls).sort(function (a, b) {
      return (+a) - (+b);
  }).slice(0, 10).reduce(function (p, c) {
      return p + this.rolls[c].reduce(function (p, c) {
          return p + c;
      }, 0);
  }, 0);
};

Game.prototype.frameHandler = function(pins) {
  if (this.frameOver) {
    this.currentFrame++; this.frameOver = !this.frameOver
  } else {
  this.frameOver = !this.frameOver;
  };
};

Game.prototype.nextFrameBonus = function(pins) {
  if (this.isSpare) {
    this.wasSpare = true;
    this.isSpare = false
    if (this.wasStrike) {
      this.wasStrike = false;
      this.wasStrike2 = true
    }
  } else if (this.isStrike && this.wasStrike) {
    this.wasStrike2 = true
  } else if (this.isStrike) {
    this.isStrike = false;
    this.wasStrike = true
  } else if (this.wasStrike) {
    this.wasStrike = false;
    this.wasStrike2 = true
  } else if (this.wasStrike2) {
    this.wasStrike2 = false
  };
};

// --------------------------------------------------

Answer 1

您遇到的第一个问题是this.rolls 是Object，而不是Array，因此for (var k in this.rolls) 不能保证按顺序枚举键。所以要解决的第一个问题是取前 10 个键，将它们转换为数字，然后对它们进行排序。这里我使用了所有原生的Array 和Object 方法：

var rolls = this.rolls;
var sum = Object
  // Get all keys
  .keys(rolls)
  // Convert string keys to integers
  .map(function (key) { return parseInt(key, 10); })
  // Sort in ascending order
  .sort()
  // Take the first 10
  .slice(0, 10)
  // Get the arrays for each key
  .map(function (key) { return rolls[key]; })
  // Merge all arrays into one array
  .reduce(function (allNumbers, array) { return allNumbers.concat(array); }, [])
  // Sum all numbers
  .reduce(function (sum, number) { return sum + (number || 0); }, 0);

Answer 2

对对象键进行排序和过滤，然后使用它们将数组归约为和

var rolls = this.rolls;
var sum = Object.keys(rolls).sort(function (a, b) {
    return (+a) - (+b);
}).slice(0, 10).reduce(function (p, c) {
    return p + rolls[c].reduce(function (p, c) {
        return p + c;
    }, 0);
}, 0);

DEMO

Answer 3

已编辑：您的示例中有一个错误。您不能在forEach 中使用this。rolls。声明它（var self = this; 或者我的版本是var rolls = this.rolls; 外面）

我建议使用以下代码来计算总和：

var sum = 0;
var rolls = this.rolls;
Object.keys(rolls).forEach(function (key, i, array) {
    if (i < 10) {
        var item = rolls[key].slice();
        while (item.length) {
            sum += item ? Number(item.shift()) : 0 + item ? Number(item.pop()) : 0;
        }
    }
});
console.log(sum, this.rolls);
this.score = sum;

有你的完整例子：

function Game() {
    this.score = 0;
    this.frameOver = false;
    this.rolls = {1: [], 2: [], 3: [], 4: [], 5: [], 6: [], 7: [], 8: [], 9: [], 10: [], 11: [], 12: []};
    this.currentFrame = 1;
    // this.lastFrameStrike = false;
    // this.lastFrameSpare = false;
    // this.isStrike = false
}

Game.prototype.roll = function (pins) {
    this.strikeOrSpare(pins);
    this.bonusDistributor(pins);
    this.rolls[this.currentFrame].push(pins);
    this.scoreUpdater(pins);
    this.frameHandler(pins);
    this.nextFrameBonus(pins);
};

// --------------------------------------------------

Game.prototype.strikeOrSpare = function (pins) {
    if (pins === 10) {
        this.isStrike = true;
        this.frameOver = true;
    }
    else if (this.rolls[this.currentFrame][0] + pins === 10) {
        this.isSpare = true;
        this.frameOver = true;
    }
};

// --------------------------------------------------

Game.prototype.bonusDistributor = function (pins) {
    if (this.wasSpare) {
        this.addToLastSpare(pins);
    }
    if (this.wasStrike) {
        this.addToLast(pins);
    }
    if (this.wasStrike2 && this.currentFrame > 1) {
        this.addToLastAgain(pins);
    }
};

// --------------------------------------------------

Game.prototype.addToLast = function (pins) {
    this.rolls[this.currentFrame - 1][0] += pins;
};

Game.prototype.addToLastAgain = function (pins) {
    this.rolls[this.currentFrame - 2][0] += pins;
};

Game.prototype.addToLastSpare = function (pins) {
    this.rolls[this.currentFrame - 1][1] += pins;
    this.wasSpare = false;
};

// --------------------------------------------------

Game.prototype.scoreUpdater = function (pins) {
    var sum = 0;
//    var self = this;
    var rolls = this.rolls;
    Object.keys(rolls).forEach(function (key, i, array) {
        if (i < 10) {
            var item = rolls[key].slice();
            while (item.length) {
                sum += item ? Number(item.shift()) : 0 + item ? Number(item.pop()) : 0;
            }
        }
    });
    console.log(sum, this.rolls);
    this.score = sum;
};

Game.prototype.frameHandler = function (pins) {
    if (this.frameOver) {
        this.currentFrame++;
        this.frameOver = !this.frameOver;
    } else {
        this.frameOver = !this.frameOver;
    }
};

Game.prototype.nextFrameBonus = function (pins) {
    if (this.isSpare) {
        this.wasSpare = true;
        this.isSpare = false;
        if (this.wasStrike) {
            this.wasStrike = false;
            this.wasStrike2 = true;
        }
    } else if (this.isStrike && this.wasStrike) {
        this.wasStrike2 = true;
    } else if (this.isStrike) {
        this.isStrike = false;
        this.wasStrike = true;
    } else if (this.wasStrike) {
        this.wasStrike = false;
        this.wasStrike2 = true;
    } else if (this.wasStrike2) {
        this.wasStrike2 = false;
    }
};
var game = new Game();
game.scoreUpdater();