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>
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
在支持es6的浏览器中,这个填充可能会有帮助。
Math.sum = (...a) => Array.prototype.reduce.call(a,(a,b) => a+b)
Math.avg = (...a) => Math.sum(...a)/a.length;
你可以在Math.sum和Math.sum之间共享相同的调用方法。avg和Math。马克斯,如
var maxOne = Math.max(1,2,3,4) // 4;
你可以用数学。总和为
var sumNum = Math.sum(1,2,3,4) // 10
或者如果你有一个数组要求和,你可以使用
var sumNum = Math.sum.apply(null,[1,2,3,4]) // 10
就像
var maxOne = Math.max.apply(null,[1,2,3,4]) // 4
只是为了好玩:
var elmt = [0, 1, 2,3, 4, 7, 8, 9, 10, 11], l = elmt.length, i = -1, sum = 0;
for (; ++i < l; sum += elmt[i])
;
document.body.appendChild(document.createTextNode('The sum of all the elements is: ' + sum + ' The average of all the elements is: ' + (sum / l)));
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