Bubble Sort only sorting part of an array

Question

I am trying to use bubble sort to sort this array,

var blocks = ["50", "90", "70", "40", "190", "110", "300", "30", "60", "245"];

But for some reason I only get 110,190,245,30,300,40,50,60,70,90 when I print out the array after sorting.

Here is the code for sorting

      $("#bubble").click(function(){

        for(var i=0; i<blocks.length; i++){
          for(var j=0; j<blocks.length-i-1; j++){
            if(blocks[j]> blocks[j+1]){
              var temp = blocks[j];
              blocks[j] = blocks[j+1];
              blocks[j+1] = temp;
            }
          }
        }
        var x = blocks.toString();
        $("#blocks_container").append(x);

});

Looks like it's sorting correctly. Why do you think it's only "part" of the array? — fdomn-m
– fdomn-m, Commented Dec 15, 2019 at 14:44
Change to var blocks = [50, 90, 70, 40, 190, 110, 300, 30, 60, 245]; - what do you get? Do you know why it's different? — fdomn-m
– fdomn-m, Commented Dec 15, 2019 at 14:45

Ori Drori · Accepted Answer · 2019-12-15 14:52:34Z

3

You are sorting strings and not numbers. When comparing by their lexical values, the 1st characters are compared, and if they are the same, the 2nd characters are compared, and so on. In this case 100 is "less" than 20, since 1 comes before 2.

If you want to compare the items by their numeric values, cast them to numbers using the + operator:

+blocks[j] > +blocks[j + 1]

Example:

var blocks = ["50", "90", "70", "40", "190", "110", "300", "30", "60", "245"];

for (var i = 0; i < blocks.length; i++) {
  for (var j = 0; j < blocks.length - i - 1; j++) {
    if (+blocks[j] > +blocks[j + 1]) {
      var temp = blocks[j];
      blocks[j] = blocks[j + 1];
      blocks[j + 1] = temp;
    }
  }
}

console.log(blocks);

edited Dec 15, 2019 at 14:52

answered Dec 15, 2019 at 14:46

Ori Drori

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StepUp · Accepted Answer · 2019-12-15 18:05:29Z

0

Sorting algorithm is okay. However, you are comparing string values and this is a reason why you've got unexpected result.

However, you can convert your string to int using + sign and map function:

blocks = blocks.map(b => +b);

And then sorting will be done correctly:

var blocks = ["50", "90", "70", "40", "190", "110", "300", "30", "60", "245"];


const bubbleSort = (blocks) => {
    blocks = blocks.map(b => +b);
 
    for (var i = 0; i < blocks.length; i++) {
       for (var j = 0; j < blocks.length - i - 1; j++) {
           if (blocks[j] > blocks[j + 1]) {
               var temp = blocks[j];
               blocks[j] = blocks[j + 1];
               blocks[j + 1] = temp;
           }
       }
     }
     return blocks;
  }

  console.log(bubbleSort(blocks));

edited Dec 15, 2019 at 18:05

answered Dec 15, 2019 at 14:50

StepUp

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