diff --git a/obr/.formatter.exs b/obr/.formatter.exs
new file mode 100644
index 0000000..d2cda26
--- /dev/null
+++ b/obr/.formatter.exs
@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]
diff --git a/obr/.gitignore b/obr/.gitignore
new file mode 100644
index 0000000..5ecbb16
--- /dev/null
+++ b/obr/.gitignore
@@ -0,0 +1,28 @@
+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+obr-*.tar
+
+# Temporary files, for example, from tests.
+/tmp/
+
+measurements*.txt
diff --git a/obr/README.md b/obr/README.md
new file mode 100644
index 0000000..45a54fb
--- /dev/null
+++ b/obr/README.md
@@ -0,0 +1,7 @@
+# One billion row challenge
+
+Naive solution with explorer.
+
+```bash
+mix obr
+```
diff --git a/obr/lib/obr.ex b/obr/lib/obr.ex
new file mode 100644
index 0000000..aba02f5
--- /dev/null
+++ b/obr/lib/obr.ex
@@ -0,0 +1,55 @@
+defmodule Obr do
+  @moduledoc """
+  One billion row challenge.
+
+  https://github.com/gunnarmorling/1brc
+  """
+
+  require Explorer.DataFrame, as: DF
+
+  @doc """
+  Read the provided file and perform calculations.
+  """
+  def process_file(filepath) do
+    filepath
+    |> DF.from_csv!(
+      header: false,
+      delimiter: ";",
+      eol_delimiter: "\n",
+      dtypes: [column_1: :string, column_2: :float]
+    )
+    |> process_dataframe()
+    |> format_results()
+  end
+
+  @doc """
+  Process the dataframe and return a list of tuples containing the station name, min, mean and max temperatures".
+  """
+  def process_dataframe(df) do
+    df
+    |> DF.group_by("column_1")
+    |> DF.summarise(min: min(column_2), mean: mean(column_2), max: max(column_2))
+    |> DF.sort_by(column_1)
+    |> DF.select(["column_1", "min", "mean", "max"])
+    |> DF.to_rows_stream()
+    |> Enum.map(fn row -> {row["column_1"], row["min"], row["mean"], row["max"]} end)
+  end
+
+  def format_results(rows) do
+    str =
+      rows
+      |> Enum.map(&format_row/1)
+      |> Enum.join(", ")
+
+    "{#{str}}"
+  end
+
+  def format_row({name, min, mean, max}) do
+    temperatures =
+      [min, mean, max]
+      |> Enum.map(&Float.ceil(&1, 1))
+      |> Enum.join("/")
+
+    "#{name}=#{temperatures}"
+  end
+end
diff --git a/obr/lib/task.ex b/obr/lib/task.ex
new file mode 100644
index 0000000..ac3b713
--- /dev/null
+++ b/obr/lib/task.ex
@@ -0,0 +1,9 @@
+defmodule Mix.Tasks.Obr do
+  use Mix.Task
+
+  def run(_) do
+    {time, res} = :timer.tc(&Obr.process_file/1, ["measurements.txt"], :second)
+    IO.puts(res)
+    IO.puts("Time elapsed: #{time} seconds")
+  end
+end
diff --git a/obr/mix.exs b/obr/mix.exs
new file mode 100644
index 0000000..102f1df
--- /dev/null
+++ b/obr/mix.exs
@@ -0,0 +1,29 @@
+defmodule Obr.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :obr,
+      version: "0.1.0",
+      elixir: "~> 1.16",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      {:explorer, "~> 0.9.0"}
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end
diff --git a/obr/mix.lock b/obr/mix.lock
new file mode 100644
index 0000000..0a2e9bb
--- /dev/null
+++ b/obr/mix.lock
@@ -0,0 +1,10 @@
+%{
+  "aws_signature": {:hex, :aws_signature, "0.3.2", "adf33bc4af00b2089b7708bf20e3246f09c639a905a619b3689f0a0a22c3ef8f", [:rebar3], [], "hexpm", "b0daf61feb4250a8ab0adea60db3e336af732ff71dd3fb22e45ae3dcbd071e44"},
+  "castore": {:hex, :castore, "1.0.8", "dedcf20ea746694647f883590b82d9e96014057aff1d44d03ec90f36a5c0dc6e", [:mix], [], "hexpm", "0b2b66d2ee742cb1d9cb8c8be3b43c3a70ee8651f37b75a8b982e036752983f1"},
+  "emmap": {:hex, :emmap, "2.0.11", "aec85ae663998329cf4343ef8d3f6b49fc1b054362e6d2689ef3314f7f36d351", [:rebar3], [], "hexpm", "10789b911658c672c62a979f34eb8d1fc3f8237a367f7d5dc3dbb3e1ebefd1c4"},
+  "explorer": {:hex, :explorer, "0.9.2", "a9598eeff8d36d88f643d14818bea1869ca70c4def61bfba22f040ee315b84b6", [:mix], [{:adbc, "~> 0.1", [hex: :adbc, repo: "hexpm", optional: true]}, {:aws_signature, "~> 0.3", [hex: :aws_signature, repo: "hexpm", optional: false]}, {:castore, "~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:flame, "~> 0.3", [hex: :flame, repo: "hexpm", optional: true]}, {:fss, "~> 0.1", [hex: :fss, repo: "hexpm", optional: false]}, {:nx, "~> 0.4", [hex: :nx, repo: "hexpm", optional: true]}, {:rustler, "~> 0.34.0", [hex: :rustler, repo: "hexpm", optional: true]}, {:rustler_precompiled, "~> 0.7", [hex: :rustler_precompiled, repo: "hexpm", optional: false]}, {:table, "~> 0.1.2", [hex: :table, repo: "hexpm", optional: false]}, {:table_rex, "~> 3.1.1 or ~> 4.0.0", [hex: :table_rex, repo: "hexpm", optional: false]}], "hexpm", "63057e318d613c1819bd8bee2d8ed4f7061c3136edc6832ad18243d28e6344eb"},
+  "fss": {:hex, :fss, "0.1.1", "9db2344dbbb5d555ce442ac7c2f82dd975b605b50d169314a20f08ed21e08642", [:mix], [], "hexpm", "78ad5955c7919c3764065b21144913df7515d52e228c09427a004afe9c1a16b0"},
+  "rustler_precompiled": {:hex, :rustler_precompiled, "0.8.0", "02d218b575d8175e80138557f46bee7af5598f29e9aff8935a6c369c0e6c47a5", [:mix], [{:castore, "~> 0.1 or ~> 1.0", [hex: :castore, repo: "hexpm", optional: false]}, {:rustler, "~> 0.23", [hex: :rustler, repo: "hexpm", optional: true]}], "hexpm", "00b1711d8d828200fe931e23bb0e72c2672a3a0ef76740e3c50433afda1965fb"},
+  "table": {:hex, :table, "0.1.2", "87ad1125f5b70c5dea0307aa633194083eb5182ec537efc94e96af08937e14a8", [:mix], [], "hexpm", "7e99bc7efef806315c7e65640724bf165c3061cdc5d854060f74468367065029"},
+  "table_rex": {:hex, :table_rex, "4.0.0", "3c613a68ebdc6d4d1e731bc973c233500974ec3993c99fcdabb210407b90959b", [:mix], [], "hexpm", "c35c4d5612ca49ebb0344ea10387da4d2afe278387d4019e4d8111e815df8f55"},
+}
diff --git a/obr/test/obr_test.exs b/obr/test/obr_test.exs
new file mode 100644
index 0000000..4f446c8
--- /dev/null
+++ b/obr/test/obr_test.exs
@@ -0,0 +1,16 @@
+defmodule ObrTest do
+  use ExUnit.Case
+  doctest Obr
+
+  test "dataframe processing is correct" do
+    df = Explorer.DataFrame.new(column_1: ["c", "b", "c", "c"], column_2: [-6.0, 3.0, 1.2, 2.0])
+    res = Obr.process_dataframe(df)
+    assert res == [{"b", 3.0, 3.0, 3.0}, {"c", -6.0, -2.8 / 3, 2.0}]
+  end
+
+  test "formatting is correct" do
+    src = [{"b", 3.0, 2.91, 4.0}, {"c", -6.0, -2.8 / 3, 2.0}]
+    str = Obr.format_results(src)
+    assert str == "{b=3.0/3.0/4.0, c=-6.0/-0.9/2.0}"
+  end
+end
diff --git a/obr/test/test_helper.exs b/obr/test/test_helper.exs
new file mode 100644
index 0000000..869559e
--- /dev/null
+++ b/obr/test/test_helper.exs
@@ -0,0 +1 @@
+ExUnit.start()