JavaScript sort of Array of arrays

Question

I have this array of arrays. I want it to be sorted by arrays' length. I use array.sort( (a, b) => a.length > b.length) );

[ 
  [],
  [ 2, 2, 2, 2, 2 ],
  [],
  [],
  [ 5 ],
  [ 3, 3, 3, 3 ],
  [],
  [],
  [ 1 ],
  [ 2, 2 ],
  [ 1 ],
  [],
  [ 4 ],
  [ 3 ],
  [ 1, 1 ],
  [],
  [ 5, 5 ],
  [],
  [],
  [ 4, 4, 4, 4, 4, 4 ],
  [],
  [ 3 ],
  [ 5 ],
  [],
  [ 5 ],
  [ 1, 1 ],
  [],
  [ 3 ],
  [],
  [],
  [],
  [],
  [ 4 ],
  [ 1 ],
  [ 4, 4, 4, 4 ],
  [],
  [ 5, 5, 5, 5 ],
  [],
  [],
  [ 3 ],
  [ 5 ],
  [ 2 ],
  [],
  [],
  [ 2 ],
  [],
  [],
  [ 1, 1, 1 ],
  [],
  [ 4 ],
  [ 3, 3, 3 ],
  [],
  [],
  [ 1, 1 ],
  [],
  [ 4, 4 ],
  [ 2, 2, 2 ],
  [],
  [ 2 ],
  [ 2 ],
  [ 4 ],
  [ 2 ],
  [ 3 ],
  [ 2 ],
  [],
  [],
  [],
  [ 5 ] ]

But after all sorting returns this. Why array of length of 6 with 4 inside it is placed in the wrong place?

[ 
  [],
  [],
  [],
  [],
  [ 5 ],
  [ 2 ],
  [],
  [],
  [ 1 ],
  [ 3 ],
  [ 1 ],
  [],
  [ 4 ],
  [ 3 ],
  [ 2 ],
  [],
  [ 4 ],
  [],
  [],
  [ 2 ],
  [],
  [ 3 ],
  [ 5 ],
  [],
  [ 5 ],
  [ 2 ],
  [],
  [ 2 ],
  [],
  [],
  [],
  [],
  [ 4 ],
  [ 1 ],
  [],
  [],
  [],
  [],
  [],
  [ 3 ],
  [ 5 ],
  [ 2 ],
  [],
  [],
  [ 2 ],
  [],
  [],
  [],
  [],
  [ 4 ],
  [],
  [ 4, 4, 4, 4, 4, 4 ],
  [ 5 ],
  [ 5, 5 ],
  [ 1, 1 ],
  [ 4, 4 ],
  [ 3, 3 ],
  [ 3, 3 ],
  [ 1, 1 ],
  [ 2, 2 ],
  [ 1, 1 ],
  [ 1, 1, 1 ],
  [ 2, 2, 2 ],
  [ 3, 3, 3 ],
  [ 5, 5, 5, 5 ],
  [ 3, 3, 3, 3 ],
  [ 4, 4, 4, 4 ],
  [ 2, 2, 2, 2, 2 ] ]

What is wrong with this?

MDN explains the return value of the comparator function here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Rob M.
– Rob M., Commented May 22, 2017 at 18:18

developer_hatch · Accepted Answer · 2017-05-22 18:17:26Z

2

To do the sort function, you have to provide the max, min equal (+1 (>0 actually), -1 (<0 actually), 0 (for equals)), the faster way is by substract the results:

arr.sort(function(a, b){
  // ASC  -> a.length - b.length
  // DESC -> b.length - a.length
  return a.length - b.length ;
});

answered May 22, 2017 at 18:17

developer_hatch

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quirimmo · Accepted Answer · 2017-05-22 18:18:17Z

2

Just use the sort function using the subtraction between lengths:

  var a = [ 
  [],
  [ 2, 2, 2, 2, 2 ],
  [],
  [],
  [ 5 ],
  [ 3, 3, 3, 3 ],
  [],
  [],
  [ 1 ],
  [ 2, 2 ],
  [ 1 ],
  [],
  [ 4 ],
  [ 3 ],
  [ 1, 1 ],
  [],
  [ 5, 5 ],
  [],
  [],
  [ 4, 4, 4, 4, 4, 4 ],
  [],
  [ 3 ],
  [ 5 ],
  [],
  [ 5 ],
  [ 1, 1 ],
  [],
  [ 3 ],
  [],
  [],
  [],
  [],
  [ 4 ],
  [ 1 ],
  [ 4, 4, 4, 4 ],
  [],
  [ 5, 5, 5, 5 ],
  [],
  [],
  [ 3 ],
  [ 5 ],
  [ 2 ],
  [],
  [],
  [ 2 ],
  [],
  [],
  [ 1, 1, 1 ],
  [],
  [ 4 ],
  [ 3, 3, 3 ],
  [],
  [],
  [ 1, 1 ],
  [],
  [ 4, 4 ],
  [ 2, 2, 2 ],
  [],
  [ 2 ],
  [ 2 ],
  [ 4 ],
  [ 2 ],
  [ 3 ],
  [ 2 ],
  [],
  [],
  [],
  [ 5 ] ];
  a.sort(function(a, b) {
  return a.length - b.length;
  });
  console.log(a);

answered May 22, 2017 at 18:18

quirimmo

10k3 gold badges33 silver badges45 bronze badges

1 Comment

quirimmo Over a year ago

That's actually the same you posted so great job to you too :)

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