過濾器和 map 陣列與 Ramda

Question

我正在使用 Ramda 在他們的類別數組中獲得'Prem League'的球隊。 我的代碼如下所示，並且可以正常工作。

import { pipe, map, filter } from 'ramda'   

const teams = [
  {name: 'Liverpool', id: '1', categories: ['Prem League']},
  {name: 'Man Utd', id: '2', categories: ['Blue Square']},
  {name: 'Sheff Utd', id: '2', categories: ['Prem League']},
]

const getTeamOptions = pipe(
    filter((team) => team.categories.includes('Prem League')),
    map((team) => ({ label: team.name, value: team.id }))
);

getTeamOptions(teams)

但是我想刪除team作為 filter 和map的參數。

我嘗試了以下但得到prop(...).includes is not a function

filter(prop('categories').includes('Prem League')),

理想情況下，我也會嘗試從map中刪除team ，但也許這不是必需的。

這些變化的原因是我一直在學習這門課程，它建議prop等作為最佳實踐。

Answer 1

您可以使用 R.includes 來檢查該值是否存在。 您可以使用 R.applySpec 生成新的 object：

 const { pipe, filter, prop, includes, map, applySpec } = R; const getTeamOptions = val => pipe( filter(pipe(prop('categories'), includes(val))), map(applySpec({ label: prop('name'), value: prop('id') })) ); const teams = [{"name":"Liverpool","id":"1","categories":["Prem League"]},{"name":"Man Utd","id":"2","categories":["Blue Square"]},{"name":"Sheff Utd","id":"2","categories":["Prem League"]}]; const result = getTeamOptions('Prem League')(teams); console.log(result);

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script>

Answer 2

這也將幫助您以無點方式使用 ramda 解決它...

 const hasPremLeague = R.where({ categories: R.includes('Prem League') }); const toOption = R.applySpec({ label: R.prop('name'), value: R.prop('id') }); const getTeamOptions = R.into([], R.compose( R.filter(hasPremLeague), R.map(toOption), )); // --- const teams = [ {name: 'Liverpool', id: '1', categories: ['Prem League']}, {name: 'Man Utd', id: '2', categories: ['Blue Square']}, {name: 'Sheff Utd', id: '2', categories: ['Prem League']}, ]; console.log( getTeamOptions(teams), );

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script>

Answer 3

const premLeague = R.equals('Prem League');
const premLeagueInArray = R.any(premLeague);
const categories = R.path(['categories']);
const isPremLeagueInArray = R.pipe(
  categories,
  premLeagueInArray,
);

const teams = [
  { name: "Liverpool", id: "1", categories: ["Prem League"] },
  { name: "Man Utd", id: "2", categories: ["Blue Square"] },
  { name: "Sheff Utd", id: "2", categories: ["Prem League"] },
];
const premLeagueTeam = [
  { name: "Liverpool", id: "1", categories: ["Prem League"] },
  { name: "Sheff Utd", id: "2", categories: ["Prem League"] },
];

const transducer = R.compose(R.filter(isPremLeagueInArray));
const getPremLeagueTeam = R.transduce(transducer, R.flip(R.append), []);

R.equals(getPremLeagueTeam(teams), premLeagueTeam);

Answer 4

您也應該考慮使用非 Ramda 選項。

這可能是也可能不是Array#flatMap的濫用，但我認為這是可以接受的：filter + map = flatMap

假設您想將 10 添加到偶數並排除奇數：

[1, 2, 3, 4].flatMap(n => n % 2 === 0 ? n + 10 : []);
//=> [12, 14]

關於無點風格，還有一點需要說明。 這很好，但有時它會妨礙您。 例如，它不允許您利用一些不錯的 ES6 結構。 例如解構：

const getTeamOptions =
  teams =>
    teams.flatMap
      ( ({name: label, id: value, categories}) =>
          categories.includes('Prem League')
            ? { label, value }
            : []
      );

getTeamOptions
  ( [ {name: 'Liverpool', id: '1', categories: ['Prem League']}
    , {name: 'Man Utd', id: '2', categories: ['Blue Square']}
    , {name: 'Sheff Utd', id: '2', categories: ['Prem League']}
    ]
  );

//=> [ {label: "Liverpool", value: "1"}
//=> , {label: "Sheff Utd", value: "2"} ]

為了完整起見，這里有一個使用Array#reduce的變體：

const getTeamOptions =
  teams =>
    teams.reduce
      ( (acc, {name: label, id: value, categories}) =>
          categories.includes('Prem League')
            ? (acc.push({ label, value }), acc)
            : acc
      , []
      );

---

不要誤會我的意思！ 拉姆達絕對是驚人的。 當我第一次遇到這個庫時，我想用它重寫我的所有代碼，然后我發現了無點風格並再次重寫了所有代碼。 最后，我完全失去了對代碼的精神控制，這是一個問題。 你應該只在 Ramda 為你服務的時候才使用它。 在這種情況下，你可以不誠實。

Answer 5

我喜歡以可組合的方式執行此操作，但目前您使用的是pipe ，所以我使用pipe執行此操作以保持一致性。 下面是一個有效的解決方案

 const teams = [ { name: 'Liverpool', id: '1', categories: ['Prem League'] }, { name: 'Man Utd', id: '2', categories: ['Blue Square'] }, { name: 'Sheff Utd', id: '2', categories: ['Prem League'] } ] const getTeamOptions = pipe( filter( pipe( prop('categories'), includes('Prem League') ) ), map( pipe( props(['name', 'id']), zipObj(['label', 'value']) ) ) ) console.log(getTeamOptions(teams))

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script> <script>const { pipe, map, filter, prop, includes, zipObj, props } = R</script>