[SOLVED] Converting Lodash's _.uniqBy() to native JavaScript

Converting Lodash's _.uniqBy() to native JavaScript

Here in this snippet I am stuck with as in _.uniqBy(array, iteratee). This

iteratee can be a function or a string at the same time
Where to put the condition to check uniqueness on the property, because the iteratee function can be anything

var sourceArray = [ { id: 1, name: 'bob' },
  { id: 1, name: 'bill' },
  { id: 1, name: 'bill' } ,
  {id: 2,name: 'silly'},
  {id: 2,name: 'billy'}]

function uniqBy (inputArray, callback) {
  return inputArray.filter(callback)
}
var inputFunc = function (item) {
  return item.name
}

// var destArray = _.uniqBy(sourceArray,'name')

var destArray = uniqBy(sourceArray, inputFunc)
console.log('destArray', destArray)

What is the solution?

Solution

An ES6 uniqBy using Map with a complexity of O(n):

const uniqBy = (arr, predicate) => {
  const cb = typeof predicate === 'function' ? predicate : (o) => o[predicate];

  return [...arr.reduce((map, item) => {
    const key = (item === null || item === undefined) ?
      item : cb(item);

    map.has(key) || map.set(key, item);

    return map;
  }, new Map()).values()];
};

const sourceArray = [
  { id: 1, name: 'bob' },
  { id: 1, name: 'bill' },
  null,
  { id: 1, name: 'bill' } ,
  { id: 2,name: 'silly'},
  { id: 2,name: 'billy'},
  null,
  undefined
];

console.log('id string: ', uniqBy(sourceArray, 'id'));

console.log('name func: ', uniqBy(sourceArray, (o) => o.name));