过滤器和 map 阵列与 Ramda

Question

我正在使用 Ramda 在他们的类别数组中获得'Prem League'的球队。 我的代码如下所示，并且可以正常工作。

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)

但是我想删除team作为 filter 和map的参数。

我尝试了以下但得到prop(...).includes is not a function

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

理想情况下，我也会尝试从map中删除team ，但也许这不是必需的。

这些变化的原因是我一直在学习这门课程，它建议prop等作为最佳实践。

Answer 1

您可以使用 R.includes 来检查该值是否存在。 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

这也将帮助您以无点方式使用 ramda 解决它...

 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

您也应该考虑使用非 Ramda 选项。

这可能是也可能不是Array#flatMap的滥用，但我认为这是可以接受的：filter + map = flatMap

假设您想将 10 添加到偶数并排除奇数：

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

关于无点风格，还有一点需要说明。 这很好，但有时它会妨碍您。 例如，它不允许您利用一些不错的 ES6 结构。 例如解构：

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"} ]

为了完整起见，这里有一个使用Array#reduce的变体：

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

---

不要误会我的意思！ 拉姆达绝对是惊人的。 当我第一次遇到这个库时，我想用它重写我的所有代码，然后我发现了无点风格并再次重写了所有代码。 最后，我完全失去了对代码的精神控制，这是一个问题。 你应该只在 Ramda 为你服务的时候才使用它。 在这种情况下，你可以不诚实。

Answer 5

我喜欢以可组合的方式执行此操作，但目前您使用的是pipe ，所以我使用pipe执行此操作以保持一致性。 下面是一个有效的解决方案

 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>