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
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. */
其他回答
我认为一个更优雅的解决方案:
const sum = times.reduce((a, b) => a + b, 0);
const avg = (sum / times.length) || 0;
console.log(`The sum is: ${sum}. The average is: ${avg}.`);
在这种情况下，我推荐D3。它是最易读的(并提供了2种不同的平均值)
let d3 = require('d3');
let array = [1,2,3,4];
let sum = d3.sum(array); //10
let mean = d3.mean(array); //2.5
let median = d3.median(array);
var sum = 0;
for( var i = 0; i < elmt.length; i++ ){
sum += parseInt( elmt[i], 10 ); //don't forget to add the base
}
var avg = sum/elmt.length;
document.write( "The sum of all the elements is: " + sum + " The average is: " + avg );
只需要遍历数组，因为您的值是字符串，所以必须先将它们转换为整数。平均值就是数值的和除以数值的个数。
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
var scores =[90, 98, 89, 100, 100, 86, 94];
var sum = 0;
var avg = 0;
for(var i = 0; i < scores.length;i++){
//Taking sum of all the arraylist
sum = sum + scores[i];
}
//Taking average
avg = sum/scores.length;
//this is the function to round a decimal no
var round = avg.toFixed();
console.log(round);
