Implement a function to filter duplicates in linear time O(n) without using Set, by using an object as a hash table.

Here is an example of a JavaScript function that filters duplicates from an array in linear time O(n), using an object as a hash table, without using Set:

function filterDuplicates(arr) {
  const seen = {};
  const result = [];

  for (let i = 0; i < arr.length; i++) {
    const item = arr[i];
    if (!seen[item]) {
      seen[item] = true;
      result.push(item);
    }
  }

  return result;
}

// Example usage:
const data = [1, 2, 3, 2, 4, 1, 5];
console.log(filterDuplicates(data)); // [1, 2, 3, 4, 5]

Here, the seen object stores already encountered elements as keys, which allows for quick checking of an element's presence and adding only unique values to the final array.