add elements of an array javascript

Question

Ok, this might be easy for some genius out there but I'm struggling...

This is for a project I'm working on with a slider, I want an array the slider can use for snap points/increments... I'm probably going about this in a mental way but its all good practice! Please help.

var frootVals = [1,2,3,4,5];
var frootInc = [];

    for (i=0; i<=frootVals.length; i++) {
            if (i == 0){
            frootInc.push(frootVals[i]);
            }
            else{
            frootInc.push(frootInc[i-1] += frootVals[i])
            }
        };

What I'm trying to do is create the new array so that its values are totals of the array elements in frootVals.

The result I'm looking for would be this:

fruitInc = [1,3,6,10,15]

Change += to + and <= to <. You can avoid the awkward if statement by initializing the array with var frootInc = [frootVals[0]]; and changing the initialization of the loop variable to i=1. — Felix Kling
– Felix Kling, Commented Sep 23, 2014 at 1:07

Segfault · Accepted Answer · 2014-09-23 01:19:21Z

1

For a different take, I like the functional approach:

var frootVals = [1,2,3,4,5];
var frootInc = [];
var acc = 0;
frootVals.forEach(function(i) {
    acc = acc + i;
    frootInc.push(acc);
});

answered Sep 23, 2014 at 1:19

Segfault

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undefined · Accepted Answer · 2014-09-23 01:13:58Z

0

var frootVals = [1,2,3,4,5]
  , frootInc = [];

// while i < length, <= will give us NaN for last iteration
for ( i = 0; i < frootVals.length; i++) {
    if (i == 0) {
        frootInc.push(frootVals[i]);
    } else {
        // rather than frootIne[ i-1 ] += ,
        // we will just add both integers and push the value
        frootInc.push( frootInc[ i-1 ] + frootVals[ i ] )
    }
 };

There were a few things wrong with your code check out the commenting in my code example. Hope it helps,

answered Sep 23, 2014 at 1:13

undefined

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Louis XIV · Accepted Answer · 2014-09-23 01:10:22Z

0

This will do:

var frootVals = [1,2,3,4,5];
var frootInc = [];

for (i=0; i < frootVals.length; i++) { // inferior to the length of the array to avoid iterating 6 times
    if (i == 0) {
        frootInc.push(frootVals[i]);
    }
    else {
        frootInc.push(frootInc[i-1] + frootVals[i]) // we add the value, we don't reassign values
    }
};

alert(JSON.stringify(frootInc));

jsfiddle here: http://jsfiddle.net/f01yceo4/

answered Sep 23, 2014 at 1:10

Louis XIV

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2 Comments

HenryDavidTHROW Over a year ago

Banging, thanks for the quick response mate :) ALSO - how comes you use JSON.stringify - if you just did the alert(frootInc) would it not show the elements properly?? because that's what I've been using.

Louis XIV Over a year ago

It's an habit. I think it's ok to use alert. You can also use console.log() and check it in the console (with the inspector of your browser). developer.chrome.com/devtools/docs/console

FreeLancr · Accepted Answer · 2014-09-23 01:15:25Z

0

change your code to:

var frootVals = [1,2,3,4,5];
var frootInc = [frootvals[0]]; //array with first item of 'frootVals' array

for (i=1; i<frootVals.length; i++) {
    frootInc.push(frootInc[i-1] + frootVals[i]); //remove '='
}

answered Sep 23, 2014 at 1:15

FreeLancr

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Comments

dandavis · Accepted Answer · 2014-09-23 01:27:47Z

0

Here's a very simple pure functional approach (no vars, side-effects, or closures needed):

[1,2,3,4,5].map(function(a){return this[0]+=a;}, [0]);
// == [1, 3, 6, 10, 15]

if you name and un-sandwich the function, you can use it over and over again, unlike a hard-coded var name, property name, or for-loop...

edited Sep 23, 2014 at 1:27

answered Sep 23, 2014 at 1:21

dandavis

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2 Comments

Segfault Over a year ago

this is good (and you get my +1) but i think using a this object with more obvious intent is better as an example, like this maybe: var a = [1,2,3,4,5].map(function(a) {return this.acc += a;}, {acc: 0} );

dandavis Over a year ago

@Segfault: fair 'nuf... the important point in my answer is keeping the function pure.

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