chore: import upstream snapshot with attribution

include/dgl/sampler.h

@@ -0,0 +1,59 @@
+/**
+ *  Copyright (c) 2018 by Contributors
+ * @file dgl/sampler.h
+ * @brief DGL sampler header.
+ */
+#ifndef DGL_SAMPLER_H_
+#define DGL_SAMPLER_H_
+
+#include <cstdlib>
+#include <ctime>
+#include <string>
+#include <vector>
+
+#include "graph_interface.h"
+#include "nodeflow.h"
+
+namespace dgl {
+
+class ImmutableGraph;
+
+class SamplerOp {
+ public:
+  /**
+   * @brief Sample a graph from the seed vertices with neighbor sampling.
+   * The neighbors are sampled with a uniform distribution.
+   *
+   * @param graph A graph for sampling.
+   * @param seeds the nodes where we should start to sample.
+   * @param edge_type the type of edges we should sample neighbors.
+   * @param num_hops the number of hops to sample neighbors.
+   * @param expand_factor the max number of neighbors to sample.
+   * @param add_self_loop whether to add self loop to the sampled subgraph
+   * @param probability the transition probability (float/double).
+   * @return a NodeFlow graph.
+   */
+  template <typename ValueType>
+  static NodeFlow NeighborSample(
+      const ImmutableGraph *graph, const std::vector<dgl_id_t> &seeds,
+      const std::string &edge_type, int num_hops, int expand_factor,
+      const bool add_self_loop, const ValueType *probability);
+
+  /**
+   * @brief Sample a graph from the seed vertices with layer sampling.
+   * The layers are sampled with a uniform distribution.
+   *
+   * @param graph A graph for sampling.
+   * @param seeds the nodes where we should start to sample.
+   * @param edge_type the type of edges we should sample neighbors.
+   * @param layer_sizes The size of layers.
+   * @return a NodeFlow graph.
+   */
+  static NodeFlow LayerUniformSample(
+      const ImmutableGraph *graph, const std::vector<dgl_id_t> &seeds,
+      const std::string &neigh_type, IdArray layer_sizes);
+};
+
+}  // namespace dgl
+
+#endif  // DGL_SAMPLER_H_