如何在不将其转换为日期类型的情况下比较scala中的字符串日期

Question

I have two string dates

a = '2021-05-23 b = '2021-04-24"

I'm trying to define a function that compares two string dates and returns true if b is one month greater than a.

Can anyone help me?

Thanks

Answer 1

The question is a little bit unclear, like do you mean the difference would be EXACTLY one month? Or does the predicate hold for the input examples you provided just because 5 - 4 = 1 ? Anyway I think the code example below will give you the idea:

import java.time.LocalDate

def isOneMonthGreater(dateString1: String, dateString2: String): Boolean = 
  (LocalDate.parse(dateString1).getMonthValue - LocalDate.parse(dateString2).getMonthValue) == 1

You can also use ChronoUnit :

import java.time.LocalDate
import java.time.temporal.ChronoUnit

val d1 = LocalDate.parse("2022-05-23")
val d2 = LocalDate.parse("2022-04-24")
val d3 = LocalDate.parse("2022-04-23")

ChronoUnit.MONTHS.between(d2, d1)
// the above expression returns 0, since 29 days is actually 0 months!
ChronoUnit.MONTHS.between(d3, d1)
// this one returns 1

Also dates as strings is not a good practice most of the time, so having inputs of actual date types is more recommended.

Update:

---

Without conversion to date, you can parse it manually and there are many many ways to do this. And one thing to keep in mind is that as mentioned in comments, there might be some edge cases, but as far as I understood, this is just to explore around the language APIs.

1. using regex. You can define the format you're sure about for the date:

val pattern = "(\\d{4})-(\\d{2})-(\\d{2})".r
val dateString = "2022-03-02"

dateString match {
  case pattern(year, month, day) => ...
}

// or
val pattern(year, month, day) = dateString

But as mentioned, this is not safe, just to show that this approach exists. 2) splitting:

dateString.split("-")

And you can deal with the array elements as you wish.