lodash takeRightWhile 从起始索引

Question

如何使用带有起始索引的 lodash 的 takeRightWhile 从数组中获取值？

这里的重点是我想从一个特定的起点向后迭代，直到满足某个参数。

我想做的例子：

const myArray = [
    {val: 'a', condition: true},
    {val: 'b', condition: false},
    {val: 'c', condition: true},
    {val: 'd', condition: true},
    {val: 'e', condition: true},
    {val: 'f', condition: true},
    {val: 'g', condition: false},
];
const startAt = 5;

const myValues = _.takeRightWhile(myArray, startAt, {return condition === true});
// --> [{val: 'c', condition: true}, {val: 'd', condition: true}, {val: 'e', condition: true}]

我查看了文档 https://lodash.com/docs/4.17.4#takeRightWhile 并不能确定这是否可行。

是否有更好的方法来做到这一点？

Answer 1

Lodash 的_.takeRightWhile() 从末尾开始，到达谓词时停止。方法签名是：

_.takeRightWhile(array, [predicate=_.identity])

而且它不接受索引。

预测函数接收以下参数 - value、index、array。 index 是当前项在数组中的位置。

要实现您的目标，请使用 _.take(startAt + 1) 将数组切割到（包括）起始索引，并使用 _.takeRightWhile()：

const myArray = [{"val":"a","condition":true},{"val":"b","condition":false},{"val":"c","condition":true},{"val":"d","condition":true},{"val":"e","condition":true},{"val":"f","condition":true},{"val":"g","condition":false}];

const startAt = 5;

const myValues = _(myArray)
  .take(startAt + 1) // take all elements including startAt
  .takeRightWhile(({ condition }) => condition) // take from the right 'till condition is false
  .value();

console.log(myValues);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

Answer 2

你可以使用 slice 和 lodash 来做到这一点

const myArray = [
    {val: 'a', condition: true},
    {val: 'b', condition: false},
    {val: 'c', condition: true},
    {val: 'd', condition: true},
    {val: 'e', condition: true},
    {val: 'f', condition: true},
    {val: 'g', condition: false},
];
const startAt = 5;

const myValues = _.takeRightWhile(myArray.slice(0, startAt), e => e.condition == true);

console.log(myValues);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js"></script>