square of two arrays numbers in javascript

Question

Function that compares and array with its numerically sorted version in ascending order. Return the sum of the square differences between each term of the two arrays.

Expample:

For the array a= [2,3,1], the sorted version is b=[1,2,3],

.the sum of the square differences is (2-1)2 + (3-2)2 + (1-3)2 = 6

. or in terms of array elements (a[0]-b[0])2 + (a[1]-b[1])2 + (a[2]+b[2])2 = 6

const arr = [2, 3, 1];

function myFunction(arr) {
  var newarr = [];
  var a = arr;
  var b = arr;
  var sum = 0;
  b.sort(function(a, b) {
    return a - b
  });

  for (var i = 0; i < b.length; i++) {
    var sub = a[i] - b[i];

    sub = sub * 2;
    sum += sub;
    newarr.push(sum);

  }
  return newarr;

}

console.log(myFunction(arr));

Why do you do `var a = arr` and `var b = arr`? Why not just `arr.sort()`? — Barmar, Jul 02 '21 at 21:02
`a` and `b` are the same array. So `var sub = a[i] - b[i]` always sets it to `0`. — Barmar, Jul 02 '21 at 21:02
Array types are pass by reference. So the change to `b` applied to `a` since they share the same reference, this is why the subtraction is always `0`. — Spencer Wieczorek, Jul 02 '21 at 21:03
`sub = sub * 2` is not how you square a number. `sub = sub * sub` squares it. — Barmar, Jul 02 '21 at 21:03
i was thing a = arr store old array and b = array b.short() so i will get old and new array. but not working. — leesa, Jul 02 '21 at 21:07

score 0 · Accepted Answer · answered Jul 02 '21 at 21:07

0

Assigning arrays doesn't make copies. So a, b, and arr are all the same array, and you're just subtracting a number from itself, always getting zero. You need to make a copy of the array in the other variable.

You're also not squaring correctly, it should be sub * sub, not sub * 2.

You're supposed to return sum. There's no need for newArr.

const arr = [2, 3, 1];

function myFunction(arr) {
  var sorted = [...arr]; // make copy
  sorted.sort(function(a, b) {
    return a - b
  });

  var sum = 0;
  for (var i = 0; i < sorted.length; i++) {
    var sub = arr[i] - sorted[i];
    sub = sub * sub;
    sum += sub;
  }
  return sum;

}

console.log(myFunction(arr));

answered Jul 02 '21 at 21:07

Barmar

741,623
53
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612

1

Do we need callback inside sort? – Tushar Shahi Jul 02 '21 at 21:09
1

Yes. The default sort compares as strings, not numbers. – Barmar Jul 02 '21 at 21:10
what is the meaning of "..." ...arr – leesa Jul 02 '21 at 21:42
See https://stackoverflow.com/questions/40731996/operator-in-javascript – Barmar Jul 02 '21 at 22:00

square of two arrays numbers in javascript

1 Answers1