我有问题添加一个数组的所有元素以及平均它们。我将如何做到这一点,并实现它与我目前的代码?元素的定义如下所示。

<script type="text/javascript">
//<![CDATA[

var i;
var elmt = new Array();

elmt[0] = "0";
elmt[1] = "1";
elmt[2] = "2";
elmt[3] = "3";
elmt[4] = "4";
elmt[5] = "7";
elmt[6] = "8";
elmt[7] = "9";
elmt[8] = "10";
elmt[9] = "11";

// Problem here
for (i = 9; i < 10; i++){
  document.write("The sum of all the elements is: " + /* Problem here */ + " The average of all the elements is: " + /* Problem here */ + "<br/>");
}   

//]]>
</script>

当前回答

如果你需要平均值并且可以跳过计算和的要求,你可以通过调用reduce来计算平均值:

// Assumes an array with only values that can be parsed to a Float
var reducer = function(cumulativeAverage, currentValue, currentIndex) {
  // 1. multiply average by currentIndex to find cumulative sum of previous elements
  // 2. add currentValue to get cumulative sum, including current element
  // 3. divide by total number of elements, including current element (zero-based index + 1)
  return (cumulativeAverage * currentIndex + parseFloat(currentValue))/(currentIndex + 1)
}
console.log([1, 2, 3, 4, 5, 6, 7, 8, 9, 10].reduce(reducer, 0)); // => 5.5
console.log([].reduce(reducer, 0)); // => 0
console.log([0].reduce(reducer, 0)); // => 0
console.log([].reduce(reducer, 0)); // => 0
console.log([,,,].reduce(reducer, 0)); // => 0
console.log([].reduce(reducer, 0)); // => 0

其他回答

如果你需要平均值并且可以跳过计算和的要求,你可以通过调用reduce来计算平均值:

// Assumes an array with only values that can be parsed to a Float
var reducer = function(cumulativeAverage, currentValue, currentIndex) {
  // 1. multiply average by currentIndex to find cumulative sum of previous elements
  // 2. add currentValue to get cumulative sum, including current element
  // 3. divide by total number of elements, including current element (zero-based index + 1)
  return (cumulativeAverage * currentIndex + parseFloat(currentValue))/(currentIndex + 1)
}
console.log([1, 2, 3, 4, 5, 6, 7, 8, 9, 10].reduce(reducer, 0)); // => 5.5
console.log([].reduce(reducer, 0)); // => 0
console.log([0].reduce(reducer, 0)); // => 0
console.log([].reduce(reducer, 0)); // => 0
console.log([,,,].reduce(reducer, 0)); // => 0
console.log([].reduce(reducer, 0)); // => 0

一般来说,平均使用一行程序减少是这样的

elements.reduce(function(sum, a,i,ar) { sum += a;  return i==ar.length-1?(ar.length==0?0:sum/ar.length):sum},0);

特别是被问到的问题

elements.reduce(function(sum, a,i,ar) { sum += parseFloat(a);  return i==ar.length-1?(ar.length==0?0:sum/ar.length):sum},0);

一个有效的版本是

elements.reduce(function(sum, a) { return sum + a },0)/(elements.length||1);

1分钟内理解Javascript数组缩减 http://www.airpair.com/javascript/javascript-array-reduce

正如gotofritz指出的数组。Reduce跳过未定义的值。 所以这里有一个解决方案:

(function average(arr){var finalstate=arr.reduce(function(state,a) { state.sum+=a;state.count+=1; return state },{sum:0,count:0}); return finalstate.sum/finalstate.count})([2,,,6])

我正好有10个元素(像例子中一样),所以我这样做:

( elmt[0] + elmt[1] + elmt[2] + elmt[3] + elmt[4] +
  elmt[5] + elmt[6] + elmt[7] + elmt[8] + elmt[9] ) / 10

ES6

Const average = arr => arr。Reduce ((p, c) => p + c, 0) / arr.length; Const result = average([4,4,5,6,6]);/ / 5 console.log(结果);

我在我的个人库中使用这些方法:

Array.prototype.sum = Array.prototype.sum || function() {
  return this.reduce(function(sum, a) { return sum + Number(a) }, 0);
}

Array.prototype.average = Array.prototype.average || function() {
  return this.sum() / (this.length || 1);
}

编辑: 要使用它们,只需询问数组的和或平均值,如下所示:

[1,2,3].sum() // = 6
[1,2,3].average() // = 2