JQuery Array made in For Loop, All Elements the Same

Question

I am very new to JQuery, so sorry if this is a naive question. I am trying to randomize an array of 3 numbers, 35 times. Each time I shuffle the array of 3-numbers and write to console, it looks like a new shuffle is produced. However, when I add each new shuffling to an array and print the entirety of its contents, it seems that the array subsists of 35 copies of the last shuffle made.

Thanks in advance!

var arr2 = [0,1,2]; 

var seedArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35]

var arr2AggregateArray = [];

for (i = 0; i < 35; i++) { 
    seed = seedArray[i];
    shuffle(arr2,seed);
    console.log(arr2);
    arr2AggregateArray[i] =  arr2;
    console.log(arr2); 
}

console.log(arr2AggregateArray);

please share copy of your shuffle function also.

Mohit Bhardwaj
– Mohit Bhardwaj

2016-04-21 05:37:55 +00:00
Commented Apr 21, 2016 at 5:37 — Mohit Bhardwaj
– Mohit Bhardwaj, Commented Apr 21, 2016 at 5:37

T.J. Crowder · Accepted Answer · 2018-09-20 07:57:02Z

This line:

arr2AggregateArray[i] =  arr2;

puts a reference to arr2 into arr2AggregateArray, not a copy. All 35 references refer to the same array:

+−−−−−−−−−−−−−−−−−−−−+  
| arr2AggregateArray |  
+−−−−−−−−−−−−−−−−−−−−+              +−−−−−−+
| 0:  *ref*          |−−−+−+−+−+−+−>| arr2 |
| 1:  *ref*          |−−/ / /   /   +−−−−−−+
| 2:  *ref*          |−−−/ /   /    | 0: 2 |
| 3:  *ref*          |−−−−/   /     | 1: 0 |
| ...                |       /      | 2: 1 |
| 34: *ref*          |−−−−−−/       +−−−−−−+
+−−−−−−−−−−−−−−−−−−−−+

You need to make a copy. In this case, since it just contains primitives (numbers), a shallow copy will do:

arr2AggregateArray[i] =  arr2.slice(0);

You haven't shown your shuffle function, so I've assumed it shuffles the array in-place. If it returns a new shuffled array, then you wouldn't need the slice above, but you'd just need to use shuffle's return value.

Collectives™ on Stack Overflow

JQuery Array made in For Loop, All Elements the Same

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related