Elixir中的日期排序列表

Question

我整理了一个小脚本来帮助我进行伤害恢复过程。它输出了我期望的结果，但是日期似乎没有按照我期望的那样排序-看起来按月/日排序是可行的，但不是按年份排序。如果仅排序日期列表而不使用结构，则结果相同。

旁注，使用https://github.com/lau/calendar填充我的日期范围。

defmodule Phase do
  defstruct day: "", weight: "" 
end

defmodule Recovery do
  alias Calendar.Date

  def phases(start_date, end_date, start_weight, increase_by) do
    # Get the range of dates
    date_range = Date.days_after_until(start_date, end_date, true) |> Enum.to_list

    # build all phases, starting at day 0
    values = do_phases(date_range, [], start_weight, increase_by)
    Enum.sort_by(values, &(&1.day))
  end

  defp do_phases([], recovery_plan, _weight, _increase_by), do: recovery_plan 
  defp do_phases([head | tail], recovery_plan, weight, increase_by) do
    v = [%Phase{day: head, weight: weight} | recovery_plan]
    do_phases(tail, v, weight + increase_by, increase_by)
  end
end

在iex中运行将输出以下内容:

iex(18)> d1 = Date.from_erl! {2016, 12, 29}
iex(19)> d2 = Date.from_erl! {2017, 1, 19}
iex(24)> Recovery.phases(d1, d2, 30, 5)
[%Phase{day: ~D[2017-01-01], weight: 45},
 %Phase{day: ~D[2017-01-02], weight: 50},
 %Phase{day: ~D[2017-01-03], weight: 55},
 %Phase{day: ~D[2017-01-04], weight: 60},
 %Phase{day: ~D[2017-01-05], weight: 65},
 %Phase{day: ~D[2017-01-06], weight: 70},
 %Phase{day: ~D[2017-01-07], weight: 75},
 %Phase{day: ~D[2017-01-08], weight: 80},
 %Phase{day: ~D[2017-01-09], weight: 85},
 %Phase{day: ~D[2017-01-10], weight: 90},
 %Phase{day: ~D[2017-01-11], weight: 95},
 %Phase{day: ~D[2017-01-12], weight: 100},
 %Phase{day: ~D[2017-01-13], weight: 105},
 %Phase{day: ~D[2017-01-14], weight: 110},
 %Phase{day: ~D[2017-01-15], weight: 115},
 %Phase{day: ~D[2017-01-16], weight: 120},
 %Phase{day: ~D[2017-01-17], weight: 125},
 %Phase{day: ~D[2017-01-18], weight: 130},
 %Phase{day: ~D[2017-01-19], weight: 135},
 %Phase{day: ~D[2016-12-29], weight: 30},
 %Phase{day: ~D[2016-12-30], weight: 35},
 %Phase{day: ~D[2016-12-31], weight: 40}]

Answer 1

似乎您正在使用的库中的日期结构看起来像这样:%Date{day: 25, month: 12, year: 2014}。在Elixir中，按字段的字母顺序通过结构的内容对结构进行比较。在这种情况下，最重要的是day，然后是month和year-与您要查找的相反。

您可以尝试将Enum.sort_by(values, &(&1.day))更改为Enum.sort_by(values, &(Date.to_erl(&1.day)))。这会将%Date{}结构转换为应该按预期排序的Erlang元组。