Lodash：如何從對象數組中獲取唯一值，然后按這些唯一值對這些對象進行排序？

Question

我正在嘗試使用Lodash從對象數組中獲取唯一值，然后使用這些值作為鍵來對對象數組進行排序。 我能夠找到解決方案，但是我不確定它是最復雜，可讀或性能最高的方式。

使用_.uniq和_.map ，我能夠從每個artist獲得唯一的country值。 然后我循環了這些價值觀，並由他們過濾artists 。

let artists = [
  { name: "Bob Jones", country: "Australia"},
  { name: "Jane Smith", country: "Australia"},
  { name: "James Good", country: "USA"},
  { name: "Jeremy Bond", country: "Japan"},
]

let countries = _.uniq(_.map(artists, 'country'))
// ["Australia", "USA", "Japan"]

let res = []

for (let i = 0; i < countries.length; i++) {
  let country = countries[i]
  let obj = {
    country: country,
    artists: artists.filter(artist => artist.country === country)
  }

  res.push(obj)
}

console.log(res)
/* [
  { country: "Australia",
    artists: [
      { name: "Bob Jones", country: "Australia"},
      { name: "Jane Smith", country: "Australia"}
    ]
  },
  { country: "USA",
    artists: [
      { name: "James Good", country: "USA"}
    ]
  },
  { country: "Japan",
    artists: [
      { name: "Jeremy Bond", country: "Japan"}
    ]
  }
]
*/

是否有任何Lodash功能可以代替for循環和對象分配？

Answer 1

使用_.groupBy()將藝術家收集到{ [country]: artists }的對象，然后使用_.map()將對象轉換為數組：

 const artists = [ { name: "Bob Jones", country: "Australia"}, { name: "Jane Smith", country: "Australia"}, { name: "James Good", country: "USA"}, { name: "Jeremy Bond", country: "Japan"}, ] const result = _.map( _.groupBy(artists, 'country'), (artists, country) => ({ country, artists }) ) console.log(result) 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.js"></script> 

與lodash / fp相同的解決方案 - 使用_.flow()生成一個函數：

 const { flow, groupBy, map, head } = _ const byCountry = flow( groupBy('country'), map(artists => ({ country: head(artists).country, artists })) ) const artists = [ { name: "Bob Jones", country: "Australia"}, { name: "Jane Smith", country: "Australia"}, { name: "James Good", country: "USA"}, { name: "Jeremy Bond", country: "Japan"}, ] const result = byCountry(artists) console.log(result) 

 <script src='https://cdn.jsdelivr.net/g/lodash@4(lodash.min.js+lodash.fp.min.js)'></script>