sample.js

function cleanUp (arr, max) {
  const cnts = {}  // keep track of what we find
  return arr.reduce((a, i) => { // loop over the array index by index
    cnts[i] = (cnts[i] || 0) + 1;  // mark that I seen the number
    if (cnts[i] <= max) {  // check to see if we are under the max
      return a.concat(i)  //if we are, add it to an arry
    }
    return a  // return the array for reduce
  }, [])
}