Question

I am trying to write a function that performs operations on an array and returns a different copy of the array and leaves the original one unchanged. I thought I could do this by declaring var array2 = array and then proceeding with the array operations. What am I doing wrong?

Here is my sample function:

var partition = function(array, p){
    var pivot = array[p];
    var length = array.length;
    // make a copy and move pivot to the front
    var array2 = array;
    array2[p] = array2[0];
    array2[0] = pivot;
    // partition the array
    var i = 1;
    for (var j = 1; j < length; j++){
        //console.log('i='+i+', j='+j)
        if (array2[j] < pivot) {
            var temp = array2[j];
            array2[j] = array2[i];
            array2[i] = temp;
            i++;
        }
    }
    //console.log('array after partitioning: ' + array)
    // swap pivot
    array2[0] = array2[i-1];
    array2[i-1] = pivot;
    var answer = {array: array2, p: i-1}
    return answer;
};

And my sample call:

var a = [3, 2, 1];
partition(a, 0);
console.log(a); // prints [1,2,3] but I want [3,2,1]

Answer 1

add this line instead of array2=array because it’s only create a reference to array not the new array2.

 var array2 =array.slice(0); //it will create a new array not the reference.

Fiddle http://jsfiddle.net/N64w3/