Fix DF.print for :struct (#840)

lib/explorer/data_frame.ex

@@ -5670,7 +5670,15 @@ defmodule Explorer.DataFrame do
 
     values =
       headers
-      |> Enum.map(&Series.to_list(df[&1]))
+      |> Enum.map(fn n ->
+        s = df[n]
+        list = Series.to_list(s)
+
+        case s.dtype do
+          {:struct, _} -> Enum.map(list, &inspect/1)
+          _ -> list
+        end
+      end)
       |> Enum.zip_with(& &1)
 
     name_type = Enum.zip_with(headers, types, fn x, y -> x <> y end)

test/explorer/data_frame_test.exs

@@ -2314,6 +2314,24 @@ defmodule Explorer.DataFrameTest do
 
              """
     end
+
+    test "works with structs" do
+      df = DF.new([%{n: %{a: 1}, m: 2}, %{n: %{a: 2}, m: 3}])
+
+      assert capture_io(fn -> DF.print(df) end) == """
+             +-------------------------------------------+
+             | Explorer DataFrame: [rows: 2, columns: 2] |
+             +------------------+------------------------+
+             |        m         |           n            |
+             |      <s64>       |      <struct[1]>       |
+             +==================+========================+
+             | 2                | %{"a" => 1}            |
+             +------------------+------------------------+
+             | 3                | %{"a" => 2}            |
+             +------------------+------------------------+
+
+             """
+    end
   end
 
   test "fetch/2" do