Add sample method to data_pipeline (#20)

fairseq2n/python/src/fairseq2n/bindings/data/data_pipeline.cc

@@ -318,6 +318,26 @@ def_data_pipeline(py::module_ &data_module)
                 return data_pipeline::round_robin(std::move(pipelines));
             },
             py::arg("pipelines"))
+        .def_static(
+            "sample",
+            [](
+                std::vector<std::reference_wrapper<data_pipeline>> &refs,
+                std::optional<std::vector<float>> weights)
+            {
+                std::vector<data_pipeline> pipelines{};
+
+                pipelines.reserve(refs.size());
+
+                std::transform(
+                    refs.begin(), refs.end(), std::back_inserter(pipelines), [](auto &r) {
+                        return std::move(r.get());
+                    });
+
+                return data_pipeline::sample(
+                    std::move(pipelines), std::move(weights));
+            },
+            py::arg("pipelines"),
+            py::arg("weights") = std::nullopt)
         .def_static(
             "constant",
             [](data example, std::optional<std::string> key)

fairseq2n/src/fairseq2n/CMakeLists.txt

@@ -38,6 +38,7 @@ target_sources(fairseq2n
         data/py.cc
         data/record_reader.cc
         data/round_robin_data_source.cc
+        data/sample_data_source.cc
         data/shard_data_source.cc
         data/shuffle_data_source.cc
         data/skip_data_source.cc

fairseq2n/src/fairseq2n/data/data_pipeline.cc

@@ -21,6 +21,7 @@
 #include "fairseq2n/data/prefetch_data_source.h"
 #include "fairseq2n/data/take_data_source.h"
 #include "fairseq2n/data/round_robin_data_source.h"
+#include "fairseq2n/data/sample_data_source.h"
 #include "fairseq2n/data/shard_data_source.h"
 #include "fairseq2n/data/shuffle_data_source.h"
 #include "fairseq2n/data/skip_data_source.h"
@@ -224,6 +225,39 @@ data_pipeline::round_robin(std::vector<data_pipeline> pipelines)
     return data_pipeline_builder{std::move(factory)};
 }
 
+data_pipeline_builder
+data_pipeline::sample(
+    std::vector<data_pipeline> pipelines,
+    std::optional<std::vector<float32>> weights)
+{
+    if (pipelines.empty())
+        throw_<std::invalid_argument>(
+            "`pipelines` does not contain any elements. Can not sample from empty set.");
+
+    bool is_broken = std::any_of(
+        pipelines.begin(), pipelines.end(), [](const data_pipeline &pipeline)
+        {
+            return pipeline.is_broken();
+        });
+    if (is_broken)
+        throw_<std::invalid_argument>(
+            "At least one of the specified data pipelines is broken and cannot be used in sample.");
+
+    if (!weights)
+        weights = std::vector<float32>(pipelines.size(), 1.0F / static_cast<float32>(pipelines.size()));
+    else if (weights.value().size() != pipelines.size())
+        throw_<std::invalid_argument>(
+            "The number of `pipelines` and the number of `weights` must be equal, but are {} and {} instead.", pipelines.size(), weights.value().size());
+
+    auto tmp = std::make_shared<std::vector<data_pipeline>>(std::move(pipelines));
+
+    auto factory = [tmp, weights=std::move(weights.value())]() mutable {
+        return std::make_unique<sample_data_source>(std::move(*tmp), std::move(weights));
+    };
+
+    return data_pipeline_builder{std::move(factory)};
+}
+
 data_pipeline_builder
 data_pipeline::constant(data example, std::optional<std::string> key)
 {

fairseq2n/src/fairseq2n/data/data_pipeline.h

@@ -83,6 +83,11 @@ class FAIRSEQ2_API data_pipeline {
     static data_pipeline_builder
     round_robin(std::vector<data_pipeline> pipelines);
 
+    static data_pipeline_builder
+    sample(
+        std::vector<data_pipeline> pipelines,
+        std::optional<std::vector<float>> weights = {});
+
     static data_pipeline_builder
     constant(data example, std::optional<std::string> key = {});
 

fairseq2n/src/fairseq2n/data/sample_data_source.cc

@@ -0,0 +1,72 @@
+// Copyright (c) Meta Platforms, Inc. and affiliates.
+// All rights reserved.
+//
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree.
+
+#include "fairseq2n/data/sample_data_source.h"
+
+#include <ATen/CPUGeneratorImpl.h>
+#include <ATen/Context.h>
+#include <ATen/Functions.h>
+
+#include <stdexcept>
+
+#include "fairseq2n/utils/tensor.h"
+
+namespace fairseq2n::detail {
+
+sample_data_source::sample_data_source(std::vector<data_pipeline> &&pipelines, std::vector<float32> &&weights)
+    : pipelines_(std::move(pipelines))
+{
+    weights_ = make_tensor_from_vector(weights, { static_cast<std::int64_t>(pipelines_.size()) });
+    generator_ = at::globalContext().defaultGenerator(c10::DeviceType::CPU);
+}
+
+std::optional<data>
+sample_data_source::next()
+{
+    if (eod_)
+        return std::nullopt;
+
+    std::optional<data> output = pipelines_[next_index()].next();
+    if (!output)
+        eod_ = true;
+
+    return output;
+}
+
+void
+sample_data_source::reset()
+{
+    eod_ = false;
+    for (data_pipeline &p : pipelines_)
+        p.reset();
+}
+
+void
+sample_data_source::record_position(tape &t) const
+{
+    t.record(eod_);
+    for (const data_pipeline &p : pipelines_)
+        p.record_position(t);
+}
+
+void
+sample_data_source::reload_position(tape &t)
+{
+    eod_ = t.read<bool>();
+    for (data_pipeline &p : pipelines_)
+        p.reload_position(t);
+}
+
+std::size_t
+sample_data_source::next_index()
+{
+    auto result = at::multinomial(weights_, 1, false, generator_)
+        .item<std::int64_t>();
+
+    return static_cast<std::size_t>(result);
+}
+
+}  // namespace fairseq2::detail

fairseq2n/src/fairseq2n/data/sample_data_source.h

@@ -0,0 +1,50 @@
+// Copyright (c) Meta Platforms, Inc. and affiliates.
+// All rights reserved.
+//
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree.
+
+#pragma once
+
+#include <memory>
+#include <vector>
+
+#include <ATen/Generator.h>
+#include <ATen/Tensor.h>
+
+#include "fairseq2n/data/data_pipeline.h"
+#include "fairseq2n/data/data_source.h"
+
+namespace fairseq2n::detail {
+
+/// @brief sample from a list of datasources
+class sample_data_source final : public data_source {
+public:
+    explicit
+    sample_data_source(std::vector<data_pipeline> &&pipelines, std::vector<float32> &&weights);
+
+    std::optional<data>
+    next() override;
+
+    void
+    reset() override;
+
+    void
+    record_position(tape &t) const override;
+
+    void
+    reload_position(tape &t) override;
+
+private:
+    std::size_t
+    next_index();
+
+private:
+    std::vector<data_pipeline> pipelines_;
+    bool eod_ = false;
+
+    at::Generator generator_;
+    at::Tensor weights_;
+};
+
+}  // namespace fairseq2::detail

fairseq2n/src/fairseq2n/utils/tensor.h

@@ -0,0 +1,31 @@
+// Copyright (c) Meta Platforms, Inc. and affiliates.
+// All rights reserved.
+//
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree.
+
+#pragma once
+
+#include <memory>
+#include <vector>
+
+#include <ATen/Tensor.h>
+
+namespace fairseq2n::detail {
+
+template <typename T>
+inline at::Tensor
+make_tensor_from_vector(
+    const std::vector<T> &src,
+    const std::initializer_list<std::int64_t> &shape) noexcept
+{
+    auto storage = std::make_shared<std::vector<T>>(src);
+
+    return at::from_blob(
+        storage->data(),
+        c10::ArrayRef<std::int64_t>(shape),
+        [storage](void*) mutable { storage.reset(); }
+    );
+}
+
+}  // namespace fairseq2::detail

src/fairseq2/data/data_pipeline.py

@@ -101,6 +101,19 @@ def round_robin(pipelines: Sequence["DataPipeline"]) -> "DataPipelineBuilder":
                 The data pipelines to round robin.
             """
 
+        @staticmethod
+        def sample(
+            pipelines: Sequence["DataPipeline"],
+            weights: Optional[Sequence[float]] = None,
+        ) -> "DataPipelineBuilder":
+            """Extract examples from ``pipelines`` by sampling based on ``weights``.
+
+            :param data_pipelines:
+                The data pipelines to sample from.
+            :param weights:
+                Desired distribution of pipelines. If None, use uniform distribution.
+            """
+
         @staticmethod
         def constant(example: Any, key: Optional[str] = None) -> "DataPipelineBuilder":
             ...