Generating a list of months between two dates? | Elixir Language | Page 1

ripe notch Dec 23, 2023, 2:16 PM

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We have Date.range/3 that allows steps to jump ahead, but this won't work on long time periods.
What I need is to be able to do for month <- Date.range(start, end) , by default it returns days. Is there a way of doing this without adding dependencies?

I could of course build my own function that takes the date and uses days_in_month to move ahead, but if there's a way of doing it that is already supported in the language that is of course preferable.

fair hemlock Dec 23, 2023, 2:26 PM

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You want to see how many months a date range covers? Can the range start at the end of the month or always at the beginning?

ripe notch Dec 23, 2023, 2:38 PM

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Always in the beginning

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I made a function like this

defp months_in_range(date, end_date) do
  case Date.compare(date, end_date) do
    :lt ->
      [Date.add(date, 0) | months_in_range(Date.add(date, Date.days_in_month(date)), end_date)]

    _ ->
      []
  end
end

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That way I can at least just get the month out of the Date

fair hemlock Dec 23, 2023, 2:40 PM

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Enum.reduce(Date.range(startdate, enddate), [], fn date, months ->
  if date.month not in months do
    [date.month | months]
  else
    months
  end
end)
``` I came up with this

ripe notch Dec 23, 2023, 2:41 PM

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I was thinking of using a reducer, but since it's over 5000 days it would be a lot of "not in"

fair hemlock Dec 23, 2023, 2:41 PM

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5000 is not a ton for the BEAM to handle, I wouldn't worry about it too much

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Unless this is super perf critical part of your application

ripe notch Dec 23, 2023, 2:43 PM

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Not very perf critical, I mean your solution does end up looking a lot nicer, so thats a win for sure

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However, I just realised, since it's multiple years I need to handle that

fair hemlock Dec 23, 2023, 2:44 PM

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Can make the date.month a tuple of month and year in my example, should work the same

#Generating a list of months between two dates?