CODEWITHSUNDEEP
javascriptloopssortingfor-loopreduce
brandongatlin
brandongatlin

Reputation: 17

JavaScript for loop stops running in the middle

I'm trying to return an array of numbers in descending order (biggest in the front).

My function seems to work but just quits in the middle.

let array = [1, 9, 8, 7, 2, 6, 3, 5];
let sorted = [];

function sortNumbers(array) {
  for (var i = 0; i < array.length; i++) {
    let max = array.reduce(function(a, b) {
      console.log(`a: ${a} b: ${b}`);
      return Math.max(a, b);
    });
    let maxIdx = array.indexOf(max);
    let biggest = array.splice(maxIdx, 1);
    sorted.push(biggest);
  }
  console.log('sorted array is: ', sorted.join(''));
  //returns 9876
}

sortNumbers(array);

Upvotes: 1

Views: 895

Answers (4)

Bhimashankar Mantur
Bhimashankar Mantur

Reputation: 199

use Underscore.Js for doing various manipulations on Arrays and Objects.

Underscore is a JavaScript library that provides a whole mess of useful functional programming helpers without extending any built-in objects

go to following the link: https://underscorejs.org/#

_.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); });

Upvotes: 0

Mark
Mark

Reputation: 92460

The problem you are having is being caused by splicing inside the loop. You change the array as you're looping through it. The quick fix is to loop through the array backwards so you set the correct length at the beginning of the loop:

for (var i = array.length; i > 0; i--) {
  // etc
}


let array = [1, 9, 8, 7, 2, 6, 3, 5];

let sorted = [];

function sortNumbers(array) {
  for (var i = array.length; i > 0; i--) {

    let max = array.reduce(function(a, b) {

      console.log(`a: ${a} b: ${b}`);
      return Math.max(a, b);

    });

    let maxIdx = array.indexOf(max);
    let biggest = array.splice(maxIdx, 1);
    sorted.push(biggest);
  }

  console.log('sorted array is: ', sorted.join('')); //returns 9876

}

sortNumbers(array);

Upvotes: 2

ggorlen
ggorlen

Reputation: 57175

As mentioned by others, it's generally risky to splice the array while looping over it. Looping backwards can help avoid issues where elements are removed and the index is thrown off, skipping elements, causing logic errors or throwing out of bounds exceptions.

Having said that, it seems you're attempting selection sort; however, if you're just trying to sort the array in reverse and join, your approach can be simplified to:

const array = [1, 9, 8, 7, 2, 6, 3, 5];

const sorted = array.sort((a, b) => b - a);

console.log(sorted.join(""));

Upvotes: 1

Nathan Stockton
Nathan Stockton

Reputation: 292

Is there a reason you're doing this yourself?

console.log(array.sort(function(a, b) { return a<b ? 1 : a>b ? -1 : 0; } ))



console.log(array.sort().reverse())

Upvotes: 0

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