从一系列日期戳中获取唯一的日期

Question

I have an array of date stamps:

let dateList = [ "2019-07-22T08:40:33.537Z", "2019-07-22T08:40:33.537Z", "2019-07-23T12:02:53.143Z", "2019-07-23T12:02:53.143Z", "2019-07-23T12:12:00.434Z", "2019-07-23T12:12:54.649Z", "2019-07-23T12:14:57.547Z", "2019-07-23T12:14:57.547Z", "2019-07-23T12:16:45.011Z", "2019-07-23T12:16:45.011Z", "2019-07-23T12:21:20.527Z", "2019-07-23T12:24:30.095Z", "2019-07-23T12:25:33.251Z", "2019-07-23T12:27:53.809Z", "2019-07-23T12:27:53.809Z" ]

And I need to get the list of unique dates from it. The following function allows me to remove duplicates.

let uniqueDates = [...new Set(dateList)];

However, it's still an array of unique time stamps. What I really need is an array of unique dates. So, if there are two timestamps of the same date, I need only one in the unique array. Can you please help how I can achieve that?

Answer 1

Map the dateList to contain only the dates (removing the time portion):

 let dateList = [ "2019-07-22T08:40:33.537Z", "2019-07-22T08:40:33.537Z", "2019-07-23T12:02:53.143Z", "2019-07-23T12:02:53.143Z", "2019-07-23T12:12:00.434Z", "2019-07-23T12:12:54.649Z", "2019-07-23T12:14:57.547Z", "2019-07-23T12:14:57.547Z", "2019-07-23T12:16:45.011Z", "2019-07-23T12:16:45.011Z", "2019-07-23T12:21:20.527Z", "2019-07-23T12:24:30.095Z", "2019-07-23T12:25:33.251Z", "2019-07-23T12:27:53.809Z", "2019-07-23T12:27:53.809Z" ] const uniqueDates = [...new Set( dateList .map((str) => str.match(/^\\d{4}-\\d{2}-\\d{2}/)[0]) )]; console.log(uniqueDates);