Accumulate multiple lists

Author: bschmeck

exercise_2.36.exs

@@ -0,0 +1,23 @@
+defmodule Accumulate do
+  def accum(_op, init, []), do: init
+  def accum(op, init, [head | tail]), do: op.(head, accum(op, init, tail))
+
+  def accum_n(_op, _init, [ [] | _tail]), do: []
+  def accum_n(op, init, list) do
+    heads = Enum.map(list, &(hd &1))
+    tails = Enum.map(list, &(tl &1))
+    [ accum(op, init, heads) | accum_n(op, init, tails) ]
+  end
+end
+
+ExUnit.start
+
+defmodule AccumulateTests do
+  use ExUnit.Case, async: true
+
+  test "it accumulates multiple sequences" do
+    sequences = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]
+    assert Accumulate.accum_n(&(&1 + &2), 0, sequences) == [22, 26, 30]
+  end
+end
+