javascript - filterfirst 和 filterlast 函数与 lodash

Question

假设我们有如下所示的一系列产品，产品按名称排序，然后按价格排序。我如何使用 lodash 获得每个类别中最便宜的产品或最昂贵的产品？我们需要类似 filterfirst 和 filterlast 的函数。

[
    {
      "productId": "123456",
      "name": "Daiper",
      "category": "Home",
      "store": "store1",
      "pricing": 10
    },
    {
      "productId": "123457",
      "name": "Daiper",
      "category": "Home",
      "store": "store2",
      "pricing": 20
    },
    {
      "productId": "123458",
      "name": "Daiper",
      "category": "Home",
      "store": "store3",
      "pricing": 30
    },
    {
      "productId": "123466",
      "name": "Paint",
      "category": "Home",
      "store": "store2",
      "pricing": 25
    },
    {
      "productId": "123467",
      "name": "Paint",
      "category": "Home",
      "store": "store1",
      "pricing": 36
    },
    {
      "productId": "123468",
      "name": "Paint",
      "category": "Home",
      "store": "store3",
      "pricing": 80
    }
]

Answer 1

您可以通过 name 属性 _.groupBy() 项目，然后将组数组 _.map() 到每个组的第一个或最后一个项目:

function filterGroups(groupIdProp, predicate) {
  return function(arr) {
    return _(arr)
      .groupBy(groupIdProp)
      .map(predicate)
      .values();
  }
}

var filterFirst = filterGroups('name', function(group) {
  return group[0];
});

var filterLast = filterGroups('name', function(group) {
  return group[group.length - 1];
})

var arr = [{
  "productId": "123456",
  "name": "Daiper",
  "category": "Home",
  "store": "store1",
  "pricing": 10
}, {
  "productId": "123457",
  "name": "Daiper",
  "category": "Home",
  "store": "store2",
  "pricing": 20
}, {
  "productId": "123458",
  "name": "Daiper",
  "category": "Home",
  "store": "store3",
  "pricing": 30
}, {
  "productId": "123466",
  "name": "Paint",
  "category": "Home",
  "store": "store2",
  "pricing": 25
}, {
  "productId": "123467",
  "name": "Paint",
  "category": "Home",
  "store": "store1",
  "pricing": 36
}, {
  "productId": "123468",
  "name": "Paint",
  "category": "Home",
  "store": "store3",
  "pricing": 80
}];

console.log('first', filterFirst(arr));

console.log('last', filterLast(arr));

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>