Question

155

Converting lodash _.uniqBy() to native javascript

rated 0 times [ 162] [ 7] / answers: 1 / hits: 20845 / 8 Years ago, fri, november 25, 2016, 12:00:00

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.

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briannar

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4 Years ago

answered 8 Years ago amari · Accepted Answer

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));