Converting lodash _.uniqBy() to native javascript

问题

Here in this snippet i am stuck 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 uniqness on the property because itratee 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)

Any leads on this will be most appreciated.

回答1:

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));

回答2:

You could use a sort ordered by name and a filter based on the neighborhood comparison like this :

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

var uniqBy = (inputArray, callback) => inputArray.sort((a,b) => callback(a) > callback(b))
.filter((x,i,arr) => i === arr.length -1 ? true : callback(x) !== callback(arr[i+1]));
var inputFunc = item => item.name;


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

来源：https://stackoverflow.com/questions/40801349/converting-lodash-uniqby-to-native-javascript