Add CountVectorizer (#315)

lib/scholar/feature_extraction/count_vectorizer.ex

@@ -0,0 +1,106 @@
+defmodule Scholar.FeatureExtraction.CountVectorizer do
+  @moduledoc """
+  A `CountVectorizer` converts already indexed collection of text documents to a matrix of token counts.
+  """
+  import Nx.Defn
+
+  opts_schema = [
+    max_token_id: [
+      type: :pos_integer,
+      required: true,
+      doc: ~S"""
+      Maximum token id in the input tensor.
+      """
+    ]
+  ]
+
+  @opts_schema NimbleOptions.new!(opts_schema)
+
+  @doc """
+  Generates a count matrix where each row corresponds to a document in the input corpus,
+  and each column corresponds to a unique token in the vocabulary of the corpus.
+
+  The input must be a 2D tensor where:
+
+  * Each row represents a document.
+  * Each document has integer values representing tokens.
+
+  The same number represents the same token in the vocabulary. Tokens should start from 0
+  and be consecutive. Negative values are ignored, making them suitable for padding.
+
+  ## Options
+
+  #{NimbleOptions.docs(@opts_schema)}
+
+  ## Examples
+
+      iex> t = Nx.tensor([[0, 1, 2], [1, 3, 4]])
+      iex> Scholar.FeatureExtraction.CountVectorizer.fit_transform(t, max_token_id: Scholar.FeatureExtraction.CountVectorizer.max_token_id(t))
+      Nx.tensor([
+          [1, 1, 1, 0, 0],
+          [0, 1, 0, 1, 1]
+        ])
+
+  With padding:
+
+      iex> t = Nx.tensor([[0, 1, -1], [1, 3, 4]])
+      iex> Scholar.FeatureExtraction.CountVectorizer.fit_transform(t, max_token_id: Scholar.FeatureExtraction.CountVectorizer.max_token_id(t))
+      Nx.tensor([
+            [1, 1, 0, 0, 0],
+            [0, 1, 0, 1, 1]
+        ])
+  """
+  deftransform fit_transform(tensor, opts \\ []) do
+    fit_transform_n(tensor, NimbleOptions.validate!(opts, @opts_schema))
+  end
+
+  @doc """
+  Computes the max_token_id option from given tensor.
+
+  This function cannot be called inside `defn` (and it will raise
+  if you try to do so).
+
+  ## Examples
+
+      iex> t = Nx.tensor([[1, -1, 2], [2, 0, 0], [0, 1, -1]])
+      iex> Scholar.FeatureExtraction.CountVectorizer.max_token_id(t)
+      2
+  """
+  def max_token_id(tensor) do
+    tensor |> Nx.reduce_max() |> Nx.to_number()
+  end
+
+  defnp fit_transform_n(tensor, opts) do
+    check_for_rank(tensor)
+    counts = Nx.broadcast(0, {Nx.axis_size(tensor, 0), opts[:max_token_id] + 1})
+
+    {_, counts} =
+      while {{i = 0, tensor}, counts}, Nx.less(i, Nx.axis_size(tensor, 0)) do
+        {_, counts} =
+          while {{j = 0, i, tensor}, counts}, Nx.less(j, Nx.axis_size(tensor, 1)) do
+            index = tensor[i][j]
+
+            counts =
+              if Nx.any(Nx.less(index, 0)),
+                do: counts,
+                else: Nx.indexed_add(counts, Nx.stack([i, index]), 1)
+
+            {{j + 1, i, tensor}, counts}
+          end
+
+        {{i + 1, tensor}, counts}
+      end
+
+    counts
+  end
+
+  defnp check_for_rank(tensor) do
+    if Nx.rank(tensor) != 2 do
+      raise ArgumentError,
+            """
+            expected tensor to have shape {num_documents, num_tokens}, \
+            got tensor with shape: #{inspect(Nx.shape(tensor))}\
+            """
+    end
+  end
+end

test/scholar/feature_extraction/count_vectorizer.ex

@@ -0,0 +1,53 @@
+defmodule Scholar.Preprocessing.CountVectorizer do
+  use Scholar.Case, async: true
+  alias Scholar.FeatureExtraction.CountVectorizer
+  doctest CountVectorizer
+
+  describe "fit_transform" do
+    test "fit_transform test" do
+      tesnsor = Nx.tensor([[2, 3, 0], [1, 4, 4]])
+
+      counts =
+        CountVectorizer.fit_transform(tesnsor,
+          max_token_id: CountVectorizer.max_token_id(tesnsor)
+        )
+
+      expected_counts = Nx.tensor([[1, 0, 1, 1, 0], [0, 1, 0, 0, 2]])
+
+      assert counts == expected_counts
+    end
+
+    test "fit_transform test - tensor with padding" do
+      tensor = Nx.tensor([[2, 3, 0], [1, 4, -1]])
+
+      counts =
+        CountVectorizer.fit_transform(tensor, max_token_id: CountVectorizer.max_token_id(tensor))
+
+      expected_counts = Nx.tensor([[1, 0, 1, 1, 0], [0, 1, 0, 0, 1]])
+
+      assert counts == expected_counts
+    end
+  end
+
+  describe "max_token_id" do
+    test "max_token_id test" do
+      tensor = Nx.tensor([[2, 3, 0], [1, 4, 4]])
+      assert CountVectorizer.max_token_id(tensor) == 4
+    end
+
+    test "max_token_id tes - tensor with padding" do
+      tensor = Nx.tensor([[2, 3, 0], [1, 4, -1]])
+      assert CountVectorizer.max_token_id(tensor) == 4
+    end
+  end
+
+  describe "errors" do
+    test "wrong input rank" do
+      assert_raise ArgumentError,
+                   "expected tensor to have shape {num_documents, num_tokens}, got tensor with shape: {3}",
+                   fn ->
+                     CountVectorizer.fit_transform(Nx.tensor([1, 2, 3]), max_token_id: 3)
+                   end
+    end
+  end
+end