Iterate first x elements of an associative array

Question

With an associative array of 12 elements;

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

what is the most effective way to get the sum of just the first 10 elements. The code below currently sums all elements;

  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

The first 10 elements being:

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

Here is the full code:

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
  };
};

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

What do you mean by first 10 elements? Can you be more specific? — thefourtheye, Oct 11 '15 at 16:07
`this.rolls` containing 12 elements, the sum of the first 10 is required — Barris, Oct 11 '15 at 16:09
We are talking about an associative array (key-value pairs) Which 10 elements do you expect? — thefourtheye, Oct 11 '15 at 16:09
@thefourtheye only sum of the values attached to the first ten keys — Barris, Oct 11 '15 at 16:11
There is no `first 10` in an object literal which is what you have. Either need proper array or define criteria for property keys needed — charlietfl, Oct 11 '15 at 16:11
@SheraliTurdiyev @Jacob @charlietfl - all of your solution work on jsfiddle, however in my local I'm getting back `Cannot read property '1' of undefined` - apologies I'm new — Barris, Oct 11 '15 at 18:47
Okay yes, to begin with this is the array: `rolls = {1: [], 2: [], 3: [], 4: [], 5: [], 6: [], 7: [], 8: [8, 9, 10], 9: [], 10: [], 11: [], 12: []};` — Barris, Oct 11 '15 at 18:53
so my tests fail because the code is trying to sum null values - please see full codebase above - `Game.prototype.scoreUpdater` does work but **only** when `this.rolls` is full, it need to get the total up to this.rolls[10] even when partially empty — Barris, Oct 11 '15 at 18:54
@Stussy. I have found your issue. Check my answer again. It has fixed — Sherali Turdiyev, Oct 11 '15 at 21:42

Jacob · Answer 1 · 2015-10-12T00:08:21.413

The first issue you'll have problems with is that this.rolls is an Object, not an Array, so for (var k in this.rolls) is not guaranteed to enumerate the keys in order. So the first problem to solve is to take those first 10 keys, convert them to numbers, and sort them. Here I'm using all native Array and Object methods:

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);

Yep, am used to using arrow functions usually. Fixed, thanks. — Jacob, Oct 12 '15 at 00:08

charlietfl · Answer 2 · 2015-10-11T22:35:01.960

1

Sort and filter object keys, then use them to reduce arrays to sums

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

edited Oct 11 '15 at 22:35

answered Oct 11 '15 at 16:33

charlietfl

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you cannot use `this.rolls` inside of `reduce()` – Sherali Turdiyev Oct 11 '15 at 22:03
1

@SheraliTurdiyev minor over site ..thx. Not sure why it merits a downvote, demo version works fine – charlietfl Oct 11 '15 at 22:35

Sherali Turdiyev · Accepted Answer · 2015-10-11T21:46:12.347

EDITED: There is one mistake in your example. You cannot use this.rolls inside of forEach. Declare it (var self = this; or my version is var rolls = this.rolls; outside)

I suggest following code for calculating sum:

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;

There is your full example:

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();

So, You should remove your downvote, now, my answer is correct — Sherali Turdiyev, Oct 11 '15 at 21:44
`.slice(0)` is faster than `.slice()` or others for cloning array. http://stackoverflow.com/a/21514254/4365315 — Sherali Turdiyev, Oct 11 '15 at 22:12
Thanks Sherali, btw it wasn't me who downvoted, your response was helpful — Barris, Oct 12 '15 at 10:28

Iterate first x elements of an associative array

3 Answers3