feat: add reconstruct method

lib/index.d.ts

@@ -107,6 +107,12 @@ export class Index {
      * @return {number} number of IDs removed.
      */
     removeIds(ids: number[]): number
+    /**
+     * Reconstructs a vector from the index.
+     * @param {number} key The key of the vector to reconstruct.
+     * @return {number[]} The reconstructed vector.
+     */
+    reconstruct(key: number): number[];
 
 }
 
@@ -133,6 +139,12 @@ export class IndexFlatL2 extends Index {
      * @param {IndexFlatL2} otherIndex The other IndexFlatL2 instance to merge from.
      */
     mergeFrom(otherIndex: IndexFlatL2): void;
+    /**
+     * Reconstructs a vector from the index.
+     * @param {number} key The key of the vector to reconstruct.
+     * @return {number[]} The reconstructed vector.
+     */
+    reconstruct(key: number): number[];
 }
 
 /**
@@ -158,4 +170,10 @@ export class IndexFlatIP extends Index {
      * @param {IndexFlatIP} otherIndex The other IndexFlatIP instance to merge from.
      */
     mergeFrom(otherIndex: IndexFlatIP): void;
+    /**
+     * Reconstructs a vector from the index.
+     * @param {number} key The key of the vector to reconstruct.
+     * @return {number[]} The reconstructed vector.
+     */
+    reconstruct(key: number): number[];
 }

src/faiss.cc

@@ -440,6 +440,52 @@ class IndexBase : public Napi::ObjectWrap<T>
     return Napi::Buffer<uint8_t>::Copy(env, writer->data.data(), writer->data.size());
   }
 
+  Napi::Value reconstruct(const Napi::CallbackInfo &info)
+  {
+    Napi::Env env = info.Env();
+
+    if (info.Length() != 1)
+    {
+      Napi::Error::New(env, "Expected 1 argument, but got " + std::to_string(info.Length()) + ".")
+          .ThrowAsJavaScriptException();
+      return env.Undefined();
+    }
+    if (!info[0].IsNumber())
+    {
+      Napi::TypeError::New(env, "Invalid argument type, must be a number.").ThrowAsJavaScriptException();
+      return env.Undefined();
+    }
+
+    const idx_t key = info[0].As<Napi::Number>().Int64Value();
+
+    if (key < 0 || key >= index_->ntotal)
+    {
+      Napi::Error::New(env, "Invalid key: " + std::to_string(key) + " (must be between 0 and " + std::to_string(index_->ntotal - 1) + ").")
+          .ThrowAsJavaScriptException();
+      return env.Undefined();
+    }
+
+    try
+    {
+      float *reconstructed = new float[index_->d];
+      index_->reconstruct(key, reconstructed);
+
+      Napi::Array result = Napi::Array::New(env, index_->d);
+      for (size_t i = 0; i < index_->d; i++)
+      {
+        result[i] = Napi::Number::New(env, reconstructed[i]);
+      }
+
+      delete[] reconstructed;
+      return result;
+    }
+    catch (const faiss::FaissException &ex)
+    {
+      Napi::Error::New(env, ex.what()).ThrowAsJavaScriptException();
+      return env.Undefined();
+    }
+  }
+
 protected:
   std::unique_ptr<faiss::Index> index_;
   inline static Napi::FunctionReference *constructor;
@@ -467,6 +513,7 @@ class Index : public IndexBase<Index, faiss::IndexFlatL2>
       InstanceMethod("mergeFrom", &Index::mergeFrom),
       InstanceMethod("removeIds", &Index::removeIds),
       InstanceMethod("toBuffer", &Index::toBuffer),
+      InstanceMethod("reconstruct", &Index::reconstruct),
       StaticMethod("read", &Index::read),
       StaticMethod("fromBuffer", &Index::fromBuffer),
       StaticMethod("fromFactory", &Index::fromFactory),
@@ -502,6 +549,7 @@ class IndexFlatL2 : public IndexBase<IndexFlatL2, faiss::IndexFlatL2>
       InstanceMethod("mergeFrom", &IndexFlatL2::mergeFrom),
       InstanceMethod("removeIds", &IndexFlatL2::removeIds),
       InstanceMethod("toBuffer", &IndexFlatL2::toBuffer),
+      InstanceMethod("reconstruct", &IndexFlatL2::reconstruct),
       StaticMethod("read", &IndexFlatL2::read),
       StaticMethod("fromBuffer", &IndexFlatL2::fromBuffer),
     });
@@ -536,6 +584,7 @@ class IndexFlatIP : public IndexBase<IndexFlatIP, faiss::IndexFlatIP>
       InstanceMethod("mergeFrom", &IndexFlatIP::mergeFrom),
       InstanceMethod("removeIds", &IndexFlatIP::removeIds),
       InstanceMethod("toBuffer", &IndexFlatIP::toBuffer),
+      InstanceMethod("reconstruct", &IndexFlatIP::reconstruct),
       StaticMethod("read", &IndexFlatIP::read),
       StaticMethod("fromBuffer", &IndexFlatIP::fromBuffer),
     });

test/reconstruct.test.js

@@ -0,0 +1,62 @@
+const { IndexFlatL2 } = require('../lib');
+
+describe('IndexFlatL2 reconstruct', () => {
+  test('should reconstruct vectors correctly', () => {
+    const dimension = 4;
+    const index = new IndexFlatL2(dimension);
+
+    const vectors = [
+      1.0, 2.0, 3.0, 4.0,
+      5.0, 6.0, 7.0, 8.0,
+      9.0, 10.0, 11.0, 12.0
+    ];
+
+    index.add(vectors);
+
+    expect(index.ntotal()).toBe(3);
+
+    const reconstructed0 = index.reconstruct(0);
+    expect(reconstructed0).toEqual([1.0, 2.0, 3.0, 4.0]);
+
+    const reconstructed1 = index.reconstruct(1);
+    expect(reconstructed1).toEqual([5.0, 6.0, 7.0, 8.0]);
+
+    const reconstructed2 = index.reconstruct(2);
+    expect(reconstructed2).toEqual([9.0, 10.0, 11.0, 12.0]);
+  });
+
+  test('should throw error for invalid key', () => {
+    const dimension = 4;
+    const index = new IndexFlatL2(dimension);
+
+    const vector = [1.0, 2.0, 3.0, 4.0];
+    index.add(vector);
+
+    expect(() => {
+      index.reconstruct(5);
+    }).toThrow();
+
+    expect(() => {
+      index.reconstruct(-1);
+    }).toThrow();
+  });
+
+  test('should work with Index class', () => {
+    const { Index } = require('../lib');
+    const dimension = 3;
+    const index = new Index(dimension);
+
+    const vectors = [
+      1.5, 2.5, 3.5,
+      4.5, 5.5, 6.5
+    ];
+
+    index.add(vectors);
+
+    const reconstructed0 = index.reconstruct(0);
+    expect(reconstructed0).toEqual([1.5, 2.5, 3.5]);
+
+    const reconstructed1 = index.reconstruct(1);
+    expect(reconstructed1).toEqual([4.5, 5.5, 6.5]);
+  });
+});