Making sense of javascript solution for sorting an array

Question

Questions : Write a JavaScript function which will take an array of numbers stored and find the second lowest and second greatest numbers.

Not sure how this solution works :

function Second_Greatest_Lowest(arr_num) {
  arr_num.sort(function(x, y) {
    return x - y;
  });
  var uniqa = [arr_num[0]];
  var result = [];

  for (var j = 1; j < arr_num.length; j++) {
    if (arr_num[j - 1] !== arr_num[j]) {
      uniqa.push(arr_num[j]);
    }
  }
  result.push(uniqa[1], uniqa[uniqa.length - 2]);
  return result.join(',');
}

I think I understand what is happening in the loop, but I'm not sure why that is necessary when later uniqa[1] is pushed into the result array. Aren't they performing the same action?

I'm very confused about what your code is doing. All you need to do is sort the array then get array[1] and array[array.length - 2]. — M-Chen-3
– M-Chen-3, Commented Nov 24, 2020 at 19:23
@M-Chen-3 this is the solution that was listed. I'm trying to understand it too. — st123
– st123, Commented Nov 24, 2020 at 19:26
The loop seems to be deduplicating the sorted list by only adding numbers to uniqa if the previous number is different from the current one. I guess to make sure uniqa[1] is not the same as uniqa[0] (and likewise for the last two numbers in the array) — rickdenhaan
– rickdenhaan, Commented Nov 24, 2020 at 19:27
@rickdenhaan but then wouldnt the number be pushed in twice? (once from the loop and once outside the loop) — st123
– st123, Commented Nov 24, 2020 at 19:31
This function is ridiculous 😂 are you sure the author knew what he was doing? Feels like it’s a mix of sorting and then removing duplicates. Why it’s pushed into the same array? No idea — Julian Kleine
– Julian Kleine, Commented Nov 24, 2020 at 19:33

John · Accepted Answer · 2020-11-24 19:32:57Z

2

var numbers = Array(5, 5,6,3,1,67,8,4,2,421,5,1,1,0,0)

function task(numbers)
{
    // Get the unique items
    numbers = numbers.filter((el, index, arr) => arr.indexOf(el) == index);

    // Sort them
    numbers = numbers.sort((a, b) => a-b);
    
    // Take the ones you want
    return Array(numbers[1], numbers.splice(-2)[0])
}

console.log("Targets: ", task(numbers))

edited Nov 24, 2020 at 19:32

answered Nov 24, 2020 at 19:29

John

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5 Comments

rickdenhaan Over a year ago

this assumes the lowest and highest numbers are unique though. Add another 0 or 421 and you'll get the wrong answer.

John Over a year ago

@rickdenhaan fixed

Δ O Over a year ago

What is the difference between .sort((a, b) => a-b) and .sort()?

John Over a year ago

@ΔO'deltazero' one is explicit so that the person asking the question can understand what is happening, and the other is shorthand.

John Over a year ago

So how filter gets the unique numbers is that it iterates all the items in the array. It checks if the index of the item is the index that is passed. If there is a duplicate item, the index will not match and so it will be excluded from the return array. For example. If you have an array of two 23s Array(23, 23) and do indexOf(23), it will always return the index 0 since 0 is the index of the first result found.

Omer Cohen · Accepted Answer · 2020-11-24 19:36:50Z

1

almost right only the validation you need to do on the array is bigger than 1.

function getSecondLowerAndHighest(arr){
    //make the array me unique numbers
    arr = [...new Set(arr)];
    //array from minimum to maximum
    arr.sort((x,y) => x - y);
    const lower = arr[1];
    //array from maximum to minimum
    arr.reverse();
    const high = arr[1];
    return {lower, high};
}

edited Nov 24, 2020 at 19:36

answered Nov 24, 2020 at 19:33

Omer Cohen

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4 Comments

John Over a year ago

Reversing an entire array just to avoid doing arr.length - 2 seems like overkill.

Omer Cohen Over a year ago

right but think bigger if you want the second and you passing a variable. always is will be x -1;

st123 Over a year ago

can you explain how arr = [...new Set(arr)] filters the array for unique numbers?

Omer Cohen Over a year ago

easy Map can only have unique keys when try to set if a number already exists is over it.

Δ O · Accepted Answer · 2020-11-24 19:32:42Z

0

const myFunction = (arr) => {
  arr = arr
    .filter((v, i, a) => a.indexOf(v) === i) // filter unique values
    .sort() // sort if needed
    
  return [arr[1], arr[arr.length-2]]
}

const [ secondLowest, secondHighest ] = myFunction([6, 3, 6, 5, 2, 1, 2, 4])
console.log(secondLowest, secondHighest)

answered Nov 24, 2020 at 19:32

Δ O

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