Javascript reduce() 直到值总和 < 变量

Question

我正在从 Javascript 中的 JSON 文件中获取一组视频持续时间（以秒为单位），为简化起见，它看起来像这样：

array = [30, 30, 30]

我想将每个值添加到先前的值直到满足条件（总和小于变量 x），然后获取新值和视频数组中的索引位置播放.

例如，如果 x=62（条件），我想添加数组中的前两个值（根据我的理解，reduce() 在这里是合适的），并且索引 = 2（第二个视频数组）。

我掌握了reduce():

var count = array.reduce(function(prev, curr, index) {
                    console.log(prev, curr, index);
                    return prev + curr;
                });

但似乎无法超越这一点..谢谢

Answer 1

您可以使用 Array#some，它会在某个条件下中断。

var array = [30, 30, 30],
    x = 62,
    index,
    sum = 0;
    
array.some(function (a, i) {
    index = i;
    if (sum + a > x) {
        return true;
    }
    sum += a;
});

console.log(index, sum);

具有紧凑的结果和此 args

var array = [30, 30, 30],
    x = 62,
    result = { index: -1, sum: 0 };
    
array.some(function (a, i) {
    this.index = i;
    if (this.sum + a > x) {
        return true;
    }
    this.sum += a;
}, result);

console.log(result);

Answer 2

你可以

    var limit = 60;
    var array = [30,30,30];
    var count = array.reduce(function(prev, curr, index) {
      var temp = prev.sum + curr;
      if (index != -1) {
        if (temp > limit) {
          prev.index = index;
        } else {
          prev.sum = temp;
        }
      }
      return prev;
    }, {
      sum: 0,
      index: -1
    });

    console.log(count);

Answer 3

这个怎么样：https://jsfiddle.net/rtcgpgk2/1/

var count = 0; //starting index
var arrayToCheck = [20, 30, 40, 20, 50]; //array to check
var condition = 100; //condition to be more than
increment(arrayToCheck, count, condition); //call function

function increment(array, index, conditionalValue) {

  var total = 0; //total to add to
  for (var i = 0; i < index; i++) { //loop through array up to index
    total += array[i]; //add value of array at index to total
  }

  if (total < conditionalValue) { //if condition is not met
    count++; //increment index
    increment(arrayToCheck, count, condition); //call function

  } else { //otherwise
    console.log('Index : ', count) //log what index condition is met
  }

}

Answer 4

// define the max outside of the reduce
var max = 20;
var hitIndex;
var count = array.reduce(function(prev, curr, index) {
                let r = prev + curr;
                // if r is less than max keep adding 
                if (r < max) { 
                 return r 
                } else {
                  // if hitIndex is undefined set it to the current index
                  hitIndex = hitIndex === undefined ? index : hitIndex;
                  return prev;
                }
            });
console.log(count, hitIndex);

这将为您留下超过最大值的第一个添加项的索引。您可以尝试使用 index - 1 作为第一个未超过它的值。

Answer 5

var a = [2,4,5,7,8];
var index;
var result = [0, 1, 2, 3].reduce(function(a, b,i) {
  var sum = a+b;
  if(sum<11){
    index=i;
    return sum;
  }
}, 2);
console.log(result,index);

Answer 6

使用 for 循环怎么样？这是没有黑客攻击的：

function sumUntil(array, threshold) {
    let i
    let result = 0

    // we loop til the end of the array
    // or right before result > threshold
    for(i = 0; i < array.length && result+array[i] < threshold; i++) {
        result += array[i]
    }

    return {
        index: i - 1, // -1 because it is incremented at the end of the last loop
        result
    }
}

console.log(
    sumUntil( [30, 30, 30], 62 ) 
) 
// {index: 1, result: 60}

奖励：将 let 替换为 var，它适用于 IE5.5

Answer 7

您可以创建一个小的实用方法reduceWhile

// Javascript reduceWhile implementation
function reduceWhile(predicate, reducer, initValue, coll) {
    return coll.reduce(function(accumulator, val) {
        if (!predicate(accumulator, val)) return accumulator;
        return reducer(accumulator, val);
    }, initValue)
};

function predicate(accumulator, val) {
    return val < 6;
}

function reducer(accumulator, val) {
    return accumulator += val;
}

var result = reduceWhile(predicate, reducer, 0, [1, 2, 3, 4, 5, 6, 7])

console.log("result", result);

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