How to edit the highest 5 values of an array in javascript?

Question

I have a single 1d array storing a series of scores. My end goal is to have the 5 highest scores with brackets around them ( e.g. (score) ) for me to then format and output onto the display. In the case where there are duplicate scores, the first occurrences would be bracketed, up to that 5 top values.

So for example: [9,8,10,9,6,8,6,5,4,4,3,3,6] would become [(9),(8),(10),(9),6,(8),6,5,4,4,8,3,8]

What I've tried so far is this:

var topvals = scores.sort((a,b) => b-a).slice(0,5);
    for(var j=0; j< scores.length; j++){
      if(topvals.length==0){
        break;
      }else if(topvals.includes(scores[j])){
        scores[j] = "(" + scores[j] + ")";
        topvals.splice(topvals.indexOf(scores[j]),1);
      }
    }

With the idea that topvals is an array containing the top 5 values, and I then loop through scores looking for those values, removing them each time.

What this results in is the first 5 values of scores having brackets around them.

I'm happy to go a completely different route with this, or just fix what I've done so far. Thanks in advance.

Answer 1

sort with indexes attached. Use index positions to change to desired format. O(N log N) for the sort.

scores = [9,8,10,9,6,8,6,5,4,4,3,3,6]
scores.map((n,i)=>({n,i})) // each object as n: number, i: index
  .sort((a,b)=>a.n-b.n).slice(-5) // sort, slice top 5
  .forEach(({i})=>scores[i]=`(${scores[i]})`) // add parens by indexes

console.log(scores)

If you have very, very large data sets and need something closer to O(N), you'll want to implement a pivot selecting algorithm. Just sorting is simpler.

Answer 2

The call to sort() sorts scores in place, which means it changes the scores array. So that is why you need to clone it first, then sort, then slice. Also you probably want to eliminate duplicates from your scores. I linked a stack overflow answer that describes how to do that. Since filter does not filter scores in place, but rather returns a new array, you don't need to explicitly call slice(0) to clone scores.

var scores = [9,8,10,9,6,8,6,5,4,4,3,3,6];

// Function from linked SO answer.
function onlyUnique(value, index, self) { 
    return self.indexOf(value) === index;
}

// Filter unique scores into copy of array, then slice the top 5.
var topvals = scores.filter(onlyUnique).sort((a,b) => b-a).slice(0,5);

for (var j=0; j< scores.length; j++) {
   if( topvals.length==0) {
        break;
   } else if(topvals.includes(scores[j])) {
        scores[j] = "(" + scores[j] + ")";
        topvals.splice(topvals.indexOf(scores[j]),1);
   }
}

Get all unique values in a JavaScript array (remove duplicates)