Added map constructor to SparseVector

Author: ankane

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.2.2 (unreleased)
+
+- Added map constructor to `SparseVector`
+
 ## 0.2.1 (2025-01-15)
 
 - Added `std::span` constructor to `Vector`

README.md

@@ -118,6 +118,13 @@ Create a sparse vector from a `std::vector<float>`
 auto vec = pgvector::SparseVector({1, 0, 2, 0, 3, 0});
 ```
 
+Or a map of non-zero elements [unreleased]
+
+```cpp
+std::unordered_map<int, float> map = {{0, 1}, {2, 2}, {4, 3}};
+auto vec = pgvector::SparseVector(map, 6);
+```
+
 Get the number of dimensions
 
 ```cpp

include/pgvector/sparsevec.hpp

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <ostream>
+#include <unordered_map>
 #include <vector>
 
 namespace pgvector {
@@ -37,6 +38,30 @@ class SparseVector {
         }
     }
 
+    /// Creates a sparse vector from a map of non-zero elements.
+    SparseVector(const std::unordered_map<int, float>& map, int dimensions) {
+        if (dimensions < 1) {
+            throw std::invalid_argument("sparsevec must have at least 1 dimension");
+        }
+        dimensions_ = dimensions;
+
+        for (auto [i, v] : map) {
+            if (i < 0 || i >= dimensions) {
+                throw std::invalid_argument("sparsevec index out of bounds");
+            }
+
+            if (v != 0) {
+                indices_.push_back(i);
+            }
+        }
+        std::sort(indices_.begin(), indices_.end());
+
+        values_.reserve(indices_.size());
+        for (auto i : indices_) {
+            values_.push_back(map.at(i));
+        }
+    }
+
     /// Returns the number of dimensions.
     int dimensions() const {
         return dimensions_;

test/main.cpp

@@ -1,4 +1,5 @@
 #include <cassert>
+#include <unordered_map>
 
 #include "../include/pgvector/halfvec.hpp"
 #include "../include/pgvector/sparsevec.hpp"
@@ -27,6 +28,14 @@ void test_sparsevec() {
     assert(vec.values() == (std::vector<float>{1, 2, 3}));
 }
 
+void test_sparsevec_map() {
+    std::unordered_map<int, float> map = {{2, 2}, {4, 3}, {3, 0}, {0, 1}};
+    auto vec = SparseVector(map, 6);
+    assert(vec.dimensions() == 6);
+    assert(vec.indices() == (std::vector<int>{0, 2, 4}));
+    assert(vec.values() == (std::vector<float>{1, 2, 3}));
+}
+
 int main() {
     test_pqxx();
     test_vector();