Empty array after pushing to another array

Question

I want to push array A to B inside cycle and then and for every iteration of B i need to delete array A and create new one. I get all data before clearing the array, but after clearing I get array B with empty values

Code :

for (i = 0; i < XArray.length; i++) {
    var pointsArray = [];

    for (j = 0; j < XArray.length; j++) {

        if (XArray[i] == XArray[j]) {
            pointsArray.push([parseFloat(YArray[i]), parseFloat(ZArray[i])]);
        }
    }

    dataSource.push({
        name: i,
        data: pointsArray
    });
    pointsArray.length = 0;
}

Felix Kling · Accepted Answer · 2013-09-30 11:32:41Z

3

The last line

pointsArray.length = 0;

removes every element in the array you created in the first line. And since all objects are assigned by reference (and arrays are objects), the data property of the object will now point to an empty array. Here is a simplified example:

var a = [1, 2];
var b = a;
a.length = 0;
console.log(b); // [] -- an empty array

So, your current code has the same effect as

dataSource.push({
    name: i,
    data: []
});

Solution: Just remove the last line and it will work as expected.

edited Sep 30, 2013 at 11:32

answered Sep 30, 2013 at 11:26

Felix Kling

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7 Comments

yuriy.stos Over a year ago

pointsCopy = pointsArray.slice(); dataSource.push({name: i, data: pointsCopy}); pointsArray.length = 0;

Felix Kling Over a year ago

@incredible_titan: I'm not sure what you mean. But you can see here in this simplified example that in, jsfiddle.net/AsTzK, you end up with empty arrays whereas if the line's removed, you don't: jsfiddle.net/AsTzK/1. If this solution doesn't work for you, then there must be something different in your code.

yuriy.stos Over a year ago

@FelixKling For example : I have source array with names of countries and other array with products. Indicies of both arrays are equal. <br/> array1:{China, China, Korea, USA, USA}, array2:{Lenovo, Asus, Samsung, Apple, Blackberry}, result : array : {{China, {Lenovo, Asus}} ...}

Felix Kling Over a year ago

@incredible_titan: I understand your code. I didn't understand what you mean by "has the same result as result without zeroing pointsArray". Does this mean it works for your or not?

yuriy.stos Over a year ago

@FelixKling. No, it doesn't. It always gives result : {{China, Lenovo}, {China, Asus} ...}. I mean that array contains not separated values

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