获取所有值的数组总和中的第n个值

Question

I have an array of elements, i need to add the every first, seven, thirteen and nineteen (70, 74, 50, 70) values and sum of them using java script.

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'];

Anyone can help? Thanks!

Answer 1

I assume from your question that you have to add them whenever they change in the array, in that case you can use:

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

Simply add them up:

 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

a simple approach would be -

  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); 

note: the use of ~~ (double tilde) here is a quick way to convert the string to a number, had the string been 12.12 this would not have been used as ~~ will remove everything after a decimal place (much like parseInt). more info in SO questions like https://stackoverflow.com/a/10841248/2737978

Answer 4

something like this might work ...

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