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
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)));
其他回答
无刷疤痕 = [1，2，3，4，5]
function avg(arr){
var sum = 0;
for (var i = 0; i < arr.length; i++) {
sum += parseFloat(arr[i])
}
return sum / i;
}
======>>>> 3
这适用于字符串作为数字或数组中的数字。
不是最快的，但最短的，在一行中使用map() & reduce():
var average = [7,14,21].map(function(x,i,arr){return x/arr.length}).reduce(function(a,b){return a + b})
似乎有无数的解决方案，但我发现这个是简洁和优雅的。
const numbers = [1,2,3,4];
const count = numbers.length;
const reducer = (adder, value) => (adder + value);
const average = numbers.map(x => x/count).reduce(reducer);
console.log(average); // 2.5
或者更简洁地说:
const numbers = [1,2,3,4];
const average = numbers.map(x => x/numbers.length).reduce((adder, value) => (adder + value));
console.log(average); // 2.5
根据您的浏览器，您可能需要执行显式函数调用，因为箭头函数不受支持:
const r = function (adder, value) {
return adder + value;
};
const m = function (x) {
return x/count;
};
const average = numbers.map(m).reduce(r);
console.log(average); // 2.5
Or:
const average1 = numbers
.map(function (x) {
return x/count;
})
.reduce(function (adder, value) {
return adder + value;
});
console.log(average1);
在常绿浏览器上，你可以使用箭头函数 Avg = [1,2,3].reduce((a,b) => (a+b);
运行10万次，for循环方法和reduce方法之间的时间差可以忽略不计。
s=Date.now();for(i=0;i<100000;i++){ n=[1,2,3]; a=n.reduce((a,b) => (a+b)) / n.length }; console.log("100k reduce took " + (Date.now()-s) + "ms."); s=Date.now();for(i=0;i<100000;i++){n=[1,2,3]; nl=n.length; a=0; for(j=nl-1;j>0;j--){a=a+n[j];} a/nl }; console.log("100k for loop took " + (Date.now()-s) + "ms."); s=Date.now();for(i=0;i<1000000;i++){n=[1,2,3]; nl=n.length; a=0; for(j=nl-1;j>0;j--){a=a+n[j];} a/nl }; console.log("1M for loop took " + (Date.now()-s) + "ms."); s=Date.now();for(i=0;i<1000000;i++){ n=[1,2,3]; a=n.reduce((a,b) => (a+b)) / n.length }; console.log("1M reduce took " + (Date.now()-s) + "ms."); /* * RESULT on Chrome 51 * 100k reduce took 26ms. * 100k for loop took 35ms. * 10M for loop took 126ms. * 10M reduce took 209ms. */
我发现Mansilla的答案工作得很好，以确保我正在做浮点数的总和，而不是使用parseFloat()字符串的拼接:
let sum = ourarray.reduce((a, b) => parseFloat(a) + parseFloat(b), 0);
let avg = (sum / ourarray.length) || 0;
console.log(sum); // print out sum
console.log(avg); // print out avg
