Algorithm for sorting array of numbers into sets in JavaScript

Suppose, we have an array of objects that contains some like this −

const arr = [
   {'item1': 144},
   {'item2': 0},
   {'item3': 366},
   {'item4': 15},
   {'item6': 366},
   {'item7': 19},
   {'item8': 211},
   {'item9': 121}
];

We are required to write a JavaScript function that takes in one such array and clusters the objects into four groups namely −

'XL', 'L', 'M', 'S'

Numbers should be distributed in these groups on the basis of their relative magnitude.

Example

The code for this will be −

const arr = [
   {'item1': 144},
   {'item2': 0},
   {'item3': 366},
   {'item4': 15},
   {'item6': 366},
   {'item7': 19},
   {'item8': 211},
   {'item9': 121}
];
const compareWithRange = (rangeArr, num) => {
   for(let i = 0; i < rangeArr.length; i++){
      if(num <= rangeArr[i] && num > rangeArr[i + 1]){
         return i;
      };
   };
   return rangeArr.length - 1;
}
const groupBySize = (arr = []) => {
   const mapping = arr => arr.map(el => el[Object.keys(el)[0]]);
   const max = Math.max(...mapping(arr));
   const range = {
      'XL': max,
      'L': (max * 3) / 4,
      'M': (max / 2),
      'S': (max / 4)
   };
   const legend = ['XL', 'L', 'M', 'S'];
   const res = {};
   arr.forEach(el => {
      const num = el[Object.keys(el)[0]];
      const index = compareWithRange(Object.keys(range).map(key => range[key]), num);
      const size = legend[index];
      if(res.hasOwnProperty(size)){
         res[size].push(Object.keys(el));
      }
      else{
         res[size] = [Object.keys(el)];
      }
   });
   return res;
};
console.log(groupBySize(arr));

Output

And the output in the console will be −

{
   M: [ [ 'item1' ], [ 'item9' ] ],
   S: [ [ 'item2' ], [ 'item4' ], [ 'item7' ] ],
   XL: [ [ 'item3' ], [ 'item6' ] ],
   L: [ [ 'item8' ] ]
}