Why is this bubblesort not working

Question

I need to sort the following array by the 2nd element of the contained tuple. The process runs through, until the last element has passed. After that I get the exception

ERROR TypeError: Cannot read property '1' of undefined

Here is my used Code:

public list:Array<[string, number]> = new Array<[string, number]>();
//{["A", 0],["B", 8], ...}
...

var sorted = false
while (!sorted){
    sorted = true;
    this.list.forEach(function (element, index, array){
      alert(element);
      if (element[1] > array[index+1][1] ) {
        array[index][1] = array[index+1][1];
        array[index+1] = element;
        sorted = false;
      }
   });
}

I can't get, why this isn't working

So you are going to have issues when you are at the last index.... — epascarello, Mar 26 '18 at 14:28
the last `index + 1` does not exist. you may exit the last loop early. — Nina Scholz, Mar 26 '18 at 14:28
You need to make sure you are not beyond the array limits when you compare with the next element. — Karim Tarabishy, Mar 26 '18 at 14:29
[debugging - How can I debug my JavaScript code?](https://stackoverflow.com/questions/988363/how-can-i-debug-my-javascript-code) — Andreas, Mar 26 '18 at 14:33

Jonas Wilms · Accepted Answer · 2018-03-26T14:40:03.660

This line:

  array[index+1][1];

causes

ERROR TypeError: Cannot read property '1' of undefined

Thats because when the iteration reaches the last index, e.g 5, it tries to take 6 from the array, which obviously does not exist. So you need to skip the last index while iterating, e.g.:

 if(array.length - 1 === index)
  return;

How i would do that:

 var sorted = false;

 while(!sorted){
   sorted = true;
   for(let index = 1; index < array.length; index++) {
      if(array[index][1] < array[index - 1][1]) {
       ([array[index], array[index - 1]] = [array[index - 1], array[index]]);
       sorted = false;
   }
 }

or much simpler:

 array.sort((a, b) => a[1] - b[1])

Why is this bubblesort not working

1 Answers1