CODEWITHSUNDEEP
javascriptjqueryarrays
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OPTIMUS PRIME

Reputation: 1325

Sum only required array elements

I need to Sum all elements of array, up to the selected value of input (first four elements in this example):

HTML:

<input id="VAL" value="4" />

<button onclick="SUM()">BUTTON</button>

SUM: <span id="bubu"></span>

JS:

var numbers = [1, 2, 3, 4, 5];

function getSum(x,y) {return x+y;}

function SUM() { 
    document.getElementById("bubu").innerHTML = numbers.reduce(getSum);
}

Now the sum of all elements work correctly. But how can I add a loop, to get only required sum?

Fiddle DEMO

Upvotes: 1

Views: 167

Answers (4)

Emeeus
Emeeus

Reputation: 5250

Using a for loop, it's pretty simple.

var numbers = [1, 2, 3, 4, 5];

let upTo = 4;

var res = 0;

for(let i = 0; i<upTo; i++){
     res += numbers[i];
}

console.log(res)

Using reduce()

var numbers = [1, 2, 3, 4, 5];

let upTo = 4;

var res = numbers.reduce((a,e,i)=>(i<upTo)?a+e:a+0)

console.log(res)

Example: https://jsfiddle.net/fsbhoe45/

Upvotes: 1

trk
trk

Reputation: 2236

You could also do this using reduce alone if you supplied a limit to handler that indicates the index up to which you need the sum for. For e.g. if you need sum up to 4 elements then limit is 3. 

function onClickHandler(limit) {
    return numbers.reduce(function (acc, val, index) {
        return index < limit ? acc : acc + val
    }, 0)
}

Hope this helps.

Upvotes: 1

zebnat
zebnat

Reputation: 521

Use the reduce index parameter: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

var numbers = [1, 2, 3, 4, 5];

window.SUM = function() { 
    var numberOfElements = document.getElementById("VAL").value;
    document.getElementById("bubu").innerHTML = numbers.reduce(function(x, y, i){
        if(i <= numberOfElements-1) {
        return x+y;
      } else {
        return x;
      }
    });
}

https://jsfiddle.net/k9vrLsnm/3/

Upvotes: 1

T.J. Crowder
T.J. Crowder

Reputation: 1074048

There are at least two ways:

  1. filter slice first, removing the values you don't want to sum up (edited because of the OP's comment "I mean the numer of elements"), or

  2. In your reduce callback, don't add y if it's not one of the values you want to include (by checking the index you receive as the third argument to the callback)

Upvotes: 4

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