Iterate over dates range (the scala way)

Question

Given a start and an end date I would like to iterate on it by day using a foreach, map or similar function. Something like

(DateTime.now to DateTime.now + 5.day         


        

Answer 1

For just iterating by day, I do:

Iterator.iterate(start) { _ + 1.day }.takeWhile(_.isBefore(end))

This has proven to be useful enough that I have a small helper object to provide an implicit and allow for a type transformation:

object IntervalIterators {
  implicit class ImplicitIterator(val interval: Interval) extends AnyVal {
    def iterateBy(step: Period): Iterator[DateTime] = Iterator.iterate(interval.start) { _ + step }
        .takeWhile(_.isBefore(interval.end))

    def iterateBy[A](step: Period, transform: DateTime => A): Iterator[A] = iterateBy(step).map(transform)

    def iterateByDay: Iterator[LocalDate] = iterateBy(1.day, { _.toLocalDate })

    def iterateByHour: Iterator[DateTime] = iterateBy(1.hour)
  }
}

Sample usage:

import IntervalIterators._

(DateTime.now to 5.day.from(DateTime.now)).iterateByDay // Iterator[LocalDate]

(30.minutes.ago to 1.hour.from(DateTime.now)).iterateBy(1.second)  // Iterator[DateTime], broken down by second