Add initial pipeline implementation

src/shogun/machine/Pipeline.cpp

@@ -0,0 +1,115 @@
+/*
+ * This software is distributed under BSD 3-clause license (see LICENSE file).
+ *
+ * Authors: Wuwei Lin
+ */
+
+#include <shogun/machine/Pipeline.h>
+
+namespace shogun
+{
+	CPipeline::CPipeline() : CMachine()
+	{
+	}
+
+	CPipeline::~CPipeline()
+	{
+		for (auto&& stage : m_stages)
+		{
+			visit([](auto&& object) { SG_UNREF(object) }, stage);
+		}
+	}
+
+	CPipeline* CPipeline::with(CTransformer* transformer)
+	{
+		REQUIRE(
+		    m_stages.empty() ||
+		        holds_alternative<CTransformer*>(m_stages.back()),
+		    "Transformers can not be placed after machines.\n");
+
+		SG_REF(transformer);
+		m_stages.emplace_back(transformer);
+
+		return this;
+	}
+
+	CPipeline* CPipeline::then(shogun::CMachine* machine)
+	{
+		REQUIRE(
+		    m_stages.empty() ||
+		        holds_alternative<CTransformer*>(m_stages.back()),
+		    "Multiple machines are added to pipeline.\n");
+
+		SG_REF(machine);
+		m_stages.emplace_back(machine);
+
+		return this;
+	}
+
+	bool CPipeline::train_machine(CFeatures* data)
+	{
+		if (train_require_labels())
+		{
+			REQUIRE(m_labels, "No labels given.\n");
+		}
+
+		for (auto&& stage : m_stages)
+		{
+			if (holds_alternative<CTransformer*>(stage))
+			{
+				auto transformer = shogun::get<CTransformer*>(stage);
+				transformer->train_require_labels()
+				    ? transformer->fit(data, m_labels)
+				    : transformer->fit(data);
+
+				data = transformer->transform(data);
+			}
+			else
+			{
+				auto machine = shogun::get<CMachine*>(stage);
+				if (machine->train_require_labels())
+					machine->set_labels(m_labels);
+				machine->train();
+			}
+		}
+		return true;
+	}
+
+	CLabels* CPipeline::apply(CFeatures* data)
+	{
+		for (auto&& stage : m_stages)
+		{
+			if (holds_alternative<CTransformer*>(stage))
+			{
+				auto transformer = shogun::get<CTransformer*>(stage);
+				data = transformer->transform(data);
+			}
+			else
+			{
+				auto machine = shogun::get<CMachine*>(stage);
+				return machine->apply(data);
+			}
+		}
+
+		return nullptr; // unreachable
+	}
+
+	bool CPipeline::train_require_labels() const
+	{
+		bool require_labels = false;
+
+		for (auto&& stage : m_stages)
+		{
+			visit(
+			    [&require_labels](auto&& fittable) {
+				    require_labels = fittable->train_require_labels();
+				},
+			    stage);
+
+			if (require_labels)
+				return require_labels;
+		}
+
+		return require_labels;
+	}
+}

src/shogun/machine/Pipeline.h

@@ -0,0 +1,41 @@
+/*
+ * This software is distributed under BSD 3-clause license (see LICENSE file).
+ *
+ * Authors: Wuwei Lin
+ */
+
+#ifndef _PIPELINE_H_
+#define _PIPELINE_H_
+
+#include <initializer_list>
+#include <shogun/base/variant.h>
+#include <shogun/machine/Machine.h>
+#include <shogun/transformer/Transformer.h>
+
+namespace shogun
+{
+	class CPipeline : public CMachine
+	{
+	public:
+		CPipeline();
+		virtual ~CPipeline();
+
+		CPipeline* with(CTransformer* transformer);
+		CPipeline* then(CMachine* machine);
+
+		virtual CLabels* apply(CFeatures* data = NULL) override;
+
+		virtual const char* get_name() const override
+		{
+			return "Pipeline";
+		}
+
+	protected:
+		virtual bool train_machine(CFeatures* data = NULL) override;
+
+		std::vector<variant<CTransformer*, CMachine*>> m_stages;
+		virtual bool train_require_labels() const override;
+	};
+}
+
+#endif