如何获取过滤后的数组项的索引

Question

I have this situation, I have an array and I need to filter it and get the indexes of the filtered items, like this example:

var arr = ['2022-05', '2023-01', '2022-04', '2022-02', '2023-08'];

I'm using this filter:

var filter = arr.filter(e => e.split("-")[0] == '2022'); //To get the values from 2022

And I get this result:

filter = ['2022-05', '2022-04', '2022-02'];

What I need to do now is to get also the index of these items, so it would be this:

filter = ['2022-05', '2022-04', '2022-02'];
index = [0,2,3]

How can I do that? Thanks.

Answer 1

Before filtering the array you can map it to a new array of objects that include the indexes.

 var arr = ['2022-05', '2023-01', '2022-04', '2022-02', '2023-08']; var output = arr.map((value, index) => ({index, value})) .filter(e => e.value.split("-")[0] == '2022'); console.log(output);

Answer 2

when matched, just add the desired index to the array

 var arr = ['2022-05', '2023-01', '2022-04', '2022-02', '2023-08']; var index = []; var filter = arr.filter((e, indx) => { const flag = e.split("-")[0] == '2022'; if (flag) { index.push(indx) } return flag; }); console.log(filter) console.log(index)

Answer 3

您可以使用indexOf方法：

filter.map(el => arr.indexOf(el));

Answer 4

You can extract the condition check into a callback function (for simplicity), then reduce over the array and push the indexes where the condition is true into the accumulator array.

 var arr = ['2022-05', '2023-01', '2022-04', '2022-02', '2023-08']; const condition = (e) => e.split("-")[0] == '2022' const filter = arr.filter(condition) const indexes = arr.reduce((a,b,i) => (condition(b) ? a.push(i) : '', a), []) console.log(filter, indexes)