消除对象数组中的重复项

Question

I'm trying to get rid of duplicates in array of objects. I want my code linear so I'm using hashtable:

output = Array.from(new Set(output.map(e => e.company)))
  .map(company => { return output.find(e => e.company === company) })

This code works properly for this array of objects:

let output = [
  { company: 'sony'},
  { company: 'sony'},
  { company: 'apple'}
]

but thing is that I want to reuse this code so I would like to move it to function which would take array output and company string. I don't know how to do that, I tried like this:

const uniq = (array, key) => {
  return Array.from(new Set(array.map( e => e[key] )))
    .map(key => { return array.find(e => e[key] === key) })
}

but this return array of two undefined.

---

Also second thing is that it's pretty complicated code for such trivial task. Isn't there some easier way to do same without losing performance?

Answer 1

This one-liner works with arbitrary objects, not necessarily key:value pairs:

 let uniqBy = (a, key) => [...new Map(a.map(x => [x[key], x]).reverse()).values()]; // let data = [ {company: 'sony', more: 1}, {company: 'apple', more: 1}, {company: 'sony', more: 2}, {company: 'sony', more: 3}, {company: 'apple', more: 3}, ] console.log(uniqBy(data, 'company'))

If you don't care about the order of the result, you can also skip .reverse() .

Answer 2

You could map the unique values and create a new object.

 const unique = (array, key) => Array.from(new Set(array.map(o => o[key])), value => ({ [key]: value })); var output = [{ company: 'sony'}, { company: 'sony'}, { company: 'apple'}]; console.log(unique(output, "company"));

Answer 3

You have naming conflicts, just rename the second key :

 let input = [{ company: "sony" }, { company: "sony" }, { company: "apple" }]; const uniq = (array, key) => { return Array.from(new Set(array.map(e => e[key]))).map(key1 => { // ^^^^ return array.find(e => e[key] === key1); // ^^^^ }); }; const result = uniq(input, "company"); console.log(result);

Answer 4

I think the issue is you are overwriting the definition of key in the .map() callback. This version - with a separate variable name for the callback parameter - seems to do what you need:

 let output = [ { company: 'sony'}, { company: 'sony'}, { company: 'apple'} ] const uniq = (array, key) => { return Array.from(new Set(array.map( e => e[key] ))).map(x => { return array.find(e => e[key] === x) }) } console.log(uniq(output, "company"));

Answer 5

You need to rename your second map parameter to something other than key , otherwise the key inside find will not be the parameter key that is passed to the function:

 let output = [ { company: 'sony'}, { company: 'sony'}, { company: 'apple'} ] const uniq = (array, key) => { return Array.from(new Set(array.map( e => e[key] ))).map(k => { return array.find(e => e[key] === k) }) } console.log(uniq(output, 'company'));

Answer 6

If you are allowed to use Lodash there is a simple way of eliminating duplicates

_.uniqBy(your_data, 'company');