Add a new read_vector() helper which reads slices

src/include/detail/linalg/tdb_io.h

@@ -373,6 +373,58 @@ std::vector<T> read_vector(
   return read_vector_helper<T>(ctx, uri, 0, 0, temporal_policy, true);
 }
 
+/**
+ * Read the contents of a TileDB array into a std::vector.
+ * @tparam T Type of data element stored.
+ * @param ctx The TileDB context.
+ * @param uri The URI of the TileDB array.
+ * @param slices The slices to read. Each slice is a pair of start and end.
+ * @param temporal_policy The temporal policy for the read.
+ * @return The vector of data.
+ */
+template <class T, typename Slice>
+std::vector<T> read_vector(
+    const tiledb::Context& ctx,
+    const std::string& uri,
+    const std::vector<std::pair<Slice, Slice>>& slices,
+    size_t total_slices_size,
+    TemporalPolicy temporal_policy = {}) {
+  if (total_slices_size == 0) {
+    return {};
+  }
+  scoped_timer _{tdb_func__ + " " + std::string{uri}};
+
+  auto array_ = tiledb_helpers::open_array(
+      tdb_func__, ctx, uri, TILEDB_READ, temporal_policy);
+  auto schema_ = array_->schema();
+
+  const size_t idx = 0;
+  auto attr = schema_.attribute(idx);
+
+  std::string attr_name = attr.name();
+
+  // Create a subarray that reads the array up to the specified subset.
+  tiledb::Subarray subarray(ctx, *array_);
+  for (const auto& slice : slices) {
+    subarray.add_range(
+        0, static_cast<int>(slice.first), static_cast<int>(slice.second));
+  }
+
+  // @todo: use something non-initializing
+  std::vector<T> data_(total_slices_size);
+
+  tiledb::Query query(ctx, *array_);
+  query.set_subarray(subarray).set_data_buffer(
+      attr_name, data_.data(), total_slices_size);
+  tiledb_helpers::submit_query(tdb_func__, uri, query);
+  _memory_data.insert_entry(tdb_func__, total_slices_size * sizeof(T));
+
+  array_->close();
+  assert(tiledb::Query::Status::COMPLETE == query.query_status());
+
+  return data_;
+}
+
 template <class T>
 auto sizes_to_indices(const std::vector<T>& sizes) {
   std::vector<T> indices(size(sizes) + 1);

src/include/test/unit_tdb_io.cc

@@ -275,3 +275,33 @@ TEST_CASE("create group", "[tdb_io]") {
 
   read_group.close();
 }
+
+TEST_CASE("read vector slices", "[tdb_io]") {
+  tiledb::Context ctx;
+  std::string uri =
+      (std::filesystem::temp_directory_path() / "tmp_vector").string();
+
+  tiledb::VFS vfs(ctx);
+  if (vfs.is_dir(uri)) {
+    vfs.remove_dir(uri);
+  }
+
+  size_t n = 100;
+  std::vector<int> vector(n);
+  std::iota(begin(vector), end(vector), 0);
+  write_vector(ctx, vector, uri);
+
+  auto result = read_vector<int>(ctx, uri);
+  CHECK(vector == result);
+
+  std::vector<std::pair<uint64_t, uint64_t>> slices;
+  slices.push_back({0, 1});    // 2 elements.
+  slices.push_back({3, 3});    // 1 element.
+  slices.push_back({50, 60});  // 11 elements
+  size_t total_slices_size = 14;
+
+  auto result_slice = read_vector<int>(ctx, uri, slices, total_slices_size);
+  auto expected =
+      std::vector<int>{0, 1, 3, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60};
+  CHECK(result_slice == expected);
+}