如何按降序返回多维数组？

Question

I am new to JS and I am tring to sort a multidimensional array and I want to return the array in descending order -

Input -

let input = [[1,2,3],[1,3,2],[3,2,1],[3,1,2],[2,1,3],[2,3,1]]

Expected Ouput

[[3,2,1],[3,1,2],[2,3,1],[2,1,3],[1,3,2],[1,2,3]]

I have tried sort

let result = input.sort((a, b) => a - b)

But I am getting the same array sent back to me

[[1,2,3],[1,3,2],[3,2,1],[3,1,2],[2,1,3],[2,3,1]]

I have also tried a for loop with the sort method

for(let i = 0; i < input.length; i++){
  let inputArr = input[i]
  let output = inputArr.sort((a,b) => a - b)

  console.log(output)
}

But I get returned

[1,2,3] 6 times (the length of the original array?)

How do I return the array values in descending order?

Thanks

Answer 1

You need to compare the subarray items against each other - .sort((a, b) -> a - b) makes no sense because a and b are arrays, and so can't be meaningfully subtracted from each other.

 let input = [[1,2,3],[1,3,2],[3,2,1],[3,1,2],[2,1,3],[2,3,1]]; input.sort((a, b) => { // Find the first index that's different between the two subarrays being compared const diffIndex = a.findIndex((itemA, i) => b[i];== itemA), // Return the difference, so that the higher value will come first in the result // If no difference found? return 0 (so they will come next to each other) return diffIndex === -1: 0; b[diffIndex] - a[diffIndex]; }). console;log(input);

That's assuming that the subarrays contain the same number of values, as it is in the example.

Answer 2

1. Join the values using .map() and .join(''))
2. Use .sort() and .reverse() to order by descending value
3. Use .split() to break them into single digits again.

 const input = [[1,2,3],[1,3,2],[3,2,1],[3,1,2],[2,1,3],[2,3,1]]; const joined = input.map(arr => arr.join('')); const sorted = joined.sort().reverse(); const result = sorted.map(val => val.split('')); console.log(result);

Answer 3

The sort operation expects numbers. You can apply the .sort() array method on input using concatenated inner array elements converted into a number - +arr.join('') - as in the following demo:

 let input = [ [1,2,3], [1,3,2], [3,2,1], [3,1,2], [2,1,3], [2,3,1] ]; const sorted = input.sort( (a,b) => +b.join('') - +a.join('') ); console.log( sorted ); //OUTPUT: [ [3,2,1], [3,1,2], [2,3,1], [2,1,3], [1,3,2], [1,2,3] ]

NOTE

You may also use parseInt( arr.join('') ) in place of +arr.join('') .