Move merge_ranges/1 to Util

lib/transit_data/glides_report/util.ex

@@ -28,6 +28,61 @@ defmodule TransitData.GlidesReport.Util do
     |> String.pad_leading(count, "0")
   end
 
+  @doc """
+  Combines any consecutive, overlapping ranges in an enumerable.
+
+  All ranges in the enumerable must have a step of 1.
+  The returned list will be sorted.
+
+      iex> ranges = [1..2, 3..8, 7..12, 7..10, 15..20]
+      iex> merge_ranges(ranges)
+      [1..2, 3..12, 15..20]
+      iex> merge_ranges(Enum.reverse(ranges)) == merge_ranges(ranges)
+      true
+      iex> merge_ranges(Enum.shuffle(ranges)) == merge_ranges(ranges)
+      true
+
+      iex> merge_ranges([1..2//1, 2..0//-1])
+      ** (ArgumentError) received range(s) with step != 1: [2..0//-1]
+
+      iex> merge_ranges([1..5//2, 3..12//3])
+      ** (ArgumentError) received range(s) with step != 1: [1..5//2, 3..12//3]
+
+      iex> merge_ranges([])
+      []
+  """
+  @spec merge_ranges(Enumerable.t(Range.t())) :: list(Range.t())
+  def merge_ranges(ranges) do
+    bad_ranges = Enum.reject(ranges, &match?(_.._//1, &1))
+
+    unless bad_ranges == [],
+      do: raise(ArgumentError, "received range(s) with step != 1: #{inspect(bad_ranges)}")
+
+    ranges
+    |> Enum.sort_by(fn l.._r//1 -> l end)
+    |> Enum.reject(&(Range.size(&1) == 0))
+    |> Enum.chunk_while(
+      nil,
+      fn
+        range, nil ->
+          {:cont, range}
+
+        range, acc_range ->
+          if Range.disjoint?(range, acc_range),
+            do: {:cont, acc_range, range},
+            else: {:cont, merge_range_pair(acc_range, range)}
+      end,
+      fn
+        nil -> {:cont, nil}
+        final_acc -> {:cont, final_acc, nil}
+      end
+    )
+  end
+
+  defp merge_range_pair(l1..r1//1, l2..r2//1) do
+    min(l1, l2)..max(r1, r2)//1
+  end
+
   @doc """
   Formats the ratio of two numbers as a percentage.
   """

reports/glides_terminal_departure_accuracy.livemd

@@ -380,28 +380,6 @@ variances = [1, 2, 3, 5, 10]
 # OVERALL VALUES #
 ##################
 
-merge_sorted_ranges = fn l1.._r1//1, _l2..r2//1 ->
-  l1..r2//1
-end
-
-# Combines any consecutive, overlapping ranges in a pre-sorted list.
-merge_ranges = fn ranges ->
-  Enum.chunk_while(
-    ranges,
-    nil,
-    fn
-      range, nil ->
-        {:cont, range}
-
-      range, acc_range ->
-        if Range.disjoint?(range, acc_range),
-          do: {:cont, acc_range, range},
-          else: {:cont, merge_sorted_ranges.(acc_range, range)}
-    end,
-    fn final_acc -> {:cont, final_acc, nil} end
-  )
-end
-
 # %{
 #   variance => %{
 #     stop_id => [actual_departure_range1, actual_departure_range2, ...]
@@ -418,9 +396,8 @@ actual_departure_windows_by_variance =
       |> Map.new(fn {stop_id, timestamps} ->
         time_ranges =
           timestamps
-          |> Enum.sort()
           |> Enum.map(fn t -> (t - variance_sec)..(t + variance_sec)//1 end)
-          |> merge_ranges.()
+          |> GlidesReport.Util.merge_ranges()
 
         {stop_id, time_ranges}
       end)
@@ -612,4 +589,4 @@ VegaLite.new(width: 500, height: 300, title: "Percent accurate by bucket size")
 |> VegaLite.encode_field(:y, "Accuracy (% of total predictions)", type: :quantitative)
 ```
 
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