获取所有值的数组总和中的第n个值

Question

我有一个元素数组，我需要使用Java脚本将每个第一个，七个，十三个和十九个（70、74、50、70）值相加并求和。

var rowSpanHeight = ['70', '70', '70', '70', '70', '70','74', '74', '74', '74', '74', '74','50', '50', '50', '50', '50', '50','70', '70', '70', '70', '70', '70'];

有人可以帮忙吗？ 谢谢！

Answer 1

我从您的问题假设，只要它们在数组中更改，就必须添加它们，在这种情况下，您可以使用：

function sumIfDifferent( inputArr ) {
    var lastNum = -1;
    var total = 0;
    for (var i = 0, l = inputArr.length; i < l; i++) {
        num = parseInt(inputArr[i], 10);
        if (num != lastNum) {
            lastNum = num;
            total+=num;
        }
    }
    return total;
}

alert(sumIfDifferent(['70', '70', '70', '70', '70', '70','74', '74', '74', '74', '74', '74','50', '50', '50', '50', '50', '50','70', '70', '70', '70', '70', '70']));

Answer 2

只需将它们加起来即可：

 var rowSpanHeight = ['70', '70', '70', '70', '70', '70','74', '74', '74', '74', '74', '74','50', '50', '50', '50', '50', '50','70', '70', '70', '70', '70', '70']; document.write(parseInt(rowSpanHeight[0]) + parseInt(rowSpanHeight[6]) + parseInt(rowSpanHeight[12]) + parseInt(rowSpanHeight[18])); 

Answer 3

一个简单的方法是-

  var rowSpanHeight = ['70', '70', '70', '70', '70', '70','74', '74', '74', '74', '74', '74','50', '50', '50', '50', '50', '50','70', '70', '70', '70', '70', '70']; var sum = ~~rowSpanHeight [0] + ~~rowSpanHeight [6] + ~~rowSpanHeight [12] + ~~rowSpanHeight [18]; console.log(sum); 

注意：这里使用~~ （双波浪号）是将字符串转换为数字的快速方法，如果字符串是12.12，则本不会使用该字符，因为~~将删除小数点后的所有内容（类似于parseInt） 。 SO问题的更多信息，例如https://stackoverflow.com/a/10841248/2737978

Answer 4

这样的事情可能会起作用...

var sum=0;
for(var a in rowSpanHeight){
    switch(a){
        case 0:
        case 6:
        case 12:
        case 18:
             sum+=parseInt(rowSpanHeight[a]);
        break;
    }
}