Implement reader/writer for CSR

Author: BenBrock

include/binsparse/binsparse.hpp

@@ -11,6 +11,70 @@
 
 namespace binsparse {
 
+// CSR Format
+
+template <typename T, typename I>
+void write_csr_matrix(std::string fname,
+                      csr_matrix<T, I> m) {
+
+  H5::H5File f(fname.c_str(), H5F_ACC_TRUNC);
+
+  std::span<T> values(m.values, m.nnz);
+  std::span<I> colind(m.colind, m.nnz);
+  std::span<I> row_ptr(m.row_ptr, m.m+1);
+
+  hdf5_tools::write_dataset(f, "values", values);
+  hdf5_tools::write_dataset(f, "indices_1", colind);
+  hdf5_tools::write_dataset(f, "pointers_to_1", row_ptr);
+
+  std::string json_string =
+  "{\n"
+  "  \"format\": \"CSR\",\n"
+  "  \"shape\": [";
+  json_string += std::to_string(m.m) + ", " + std::to_string(m.n) +
+  "],\n" +
+  "  \"nnz\": " + std::to_string(m.nnz) + "\n" +
+  "}\n";
+
+  hdf5_tools::write_dataset(f, "metadata", json_string);
+
+  f.close();
+}
+
+template <typename T, typename I, typename Allocator>
+csr_matrix<T, I> read_csr_matrix(std::string fname, Allocator&& alloc) {
+  H5::H5File f(fname.c_str(), H5F_ACC_RDWR);
+
+  auto metadata = hdf5_tools::read_dataset<char>(f, "metadata");
+
+  using json = nlohmann::json;
+  auto data = json::parse(metadata);
+
+  if (data["format"] == "CSR") {
+    auto nrows = data["shape"][0];
+    auto ncols = data["shape"][1];
+    auto nnz = data["nnz"];
+
+    typename std::allocator_traits<std::remove_cvref_t<Allocator>>
+       :: template rebind_alloc<I> i_alloc(alloc);
+
+    auto values = hdf5_tools::read_dataset<T>(f, "values", alloc);
+    auto colind = hdf5_tools::read_dataset<I>(f, "indices_1", i_alloc);
+    auto row_ptr = hdf5_tools::read_dataset<I>(f, "pointers_to_1", i_alloc);
+
+    return csr_matrix<T, I>{values.data(), colind.data(), row_ptr.data(), nrows, ncols, nnz};
+  } else {
+    assert(false);
+  }
+}
+
+template <typename T, typename I>
+csr_matrix<T, I> read_csr_matrix(std::string fname) {
+  return read_csr_matrix<T, I>(fname, std::allocator<T>{});
+}
+
+// COO Format
+
 template <typename T, typename I>
 void write_coo_matrix(std::string fname,
                       coo_matrix<T, I> m) {