kata-5-solution-delete-occurences-conditionally.js

// ************************************************************************************
// https://www.codewars.com/kata/554ca54ffa7d91b236000023/javascript

// Alice and Bob were on a holiday. Both of them took many pictures of the places 
// they've been, and now they want to show Charlie their entire collection. 
// However, Charlie doesn't like this sessions, since the motive usually repeats. 
// He isn't fond of seeing the Eiffel tower 40 times. He tells them that he will 
// only sit during the session if they show the same motive at most N times. 
// Luckily, Alice and Bob are able to encode the motive as a number. 
// Can you help them to remove numbers such that their list contains each number 
// only up to N times, without changing the order?

// Task
// Given a list lst and a number N, create a new list that contains each 
// number of lst at most N times without reordering. For example if N = 2, 
// and the input is [1,2,3,1,2,1,2,3], you take [1,2,3,1,2], drop the next [1,2] 
// since this would lead to 1 and 2 being in the result 3 times, and then take 3, 
// which leads to [1,2,3,1,2,3].

// Example
// deleteNth ([1,1,1,1],2) // return [1,1]
// deleteNth ([20,37,20,21],1) // return [20,37,21]
// ************************************************************************************


function deleteNth(arr,allowedTimes){
  const obj = {};
   return arr.filter(elem => {
    //  if there is already key the same as elem, 
     if(obj[elem]){
      //  add +1 to the count
       obj[elem] ++;
     } else {
      //  otherwise create a key and add it value equal to 1
       obj[elem] = 1;
     }
     // filter out only elements that satify the condition
    return obj[elem] <= allowedTimes
  });
}

// deleteNth ([1,1,1,1],2) // return [1,1]
deleteNth ([20,37,20,21],1) // return [20,37,21]