Get nth value in array sum of all values

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!

Are all the repeated values always consecutive ? What have you tried so far ? — axelduch, Nov 07 '14 at 15:30
Why dont you just use the indices and then calculate the sum? — Jonas, Nov 07 '14 at 15:31

Jonas Grumann · Accepted Answer · 2014-11-07T15:41:20.217

2

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']));

edited Nov 07 '14 at 15:41

answered Nov 07 '14 at 15:33

Jonas Grumann

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Finally someone gets the generic answer. – axelduch Nov 07 '14 at 15:37
Avoid using parseInt without the radix parameter (10 here), or use directly a bitwise operator : `num = inputArr[i] | 0` – axelduch Nov 07 '14 at 15:38

score 1 · Answer 2 · answered Nov 07 '14 at 15:32

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]));

score 0 · Answer 3 · edited May 23 '17 at 12:12

0

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

edited May 23 '17 at 12:12

Community

1
1

answered Nov 07 '14 at 15:31

Quince

14,790
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dude....... double bitwise nots for someone who doesn't understand how to access an array element by index? ;) – p e p Nov 07 '14 at 15:34
yep i was just going to edit it then saw someone else had already posted the same with parseInt so figured would leave it as another option – Quince Nov 07 '14 at 15:35
Totally kidding by the way. – p e p Nov 07 '14 at 15:36
nah it's what i though after i posted it and saw I started the answer with the phrase 'simple approach' :) – Quince Nov 07 '14 at 15:38

score 0 · Answer 4 · answered Nov 07 '14 at 15:32

0

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;
    }
}

answered Nov 07 '14 at 15:32

Adam MacDonald

1,958
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Get nth value in array sum of all values

4 Answers4