Fix scalar_at in example (#7471)

## Summary

Semantic merge.

## Testing

N/A

Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>

Author: connortsui20

vortex/examples/turboquant_vector_search.rs

@@ -77,7 +77,7 @@ use vortex_tensor::vector::Vector;
 
 /// Cosine threshold for the demo filter. The query comes from the test split, so it may or may not
 /// have nearby rows in the train split.
-const COSINE_THRESHOLD: f32 = 0.90;
+const COSINE_THRESHOLD: f32 = 0.85;
 
 /// Slack for checking decoded rows against a predicate that was evaluated on TurboQuant's lossy
 /// readthrough representation.
@@ -99,13 +99,14 @@ async fn main() -> Result<()> {
 
     let session = VortexSession::default().with_tokio();
     vortex_tensor::initialize(&session);
+    let mut ctx = session.create_execution_ctx();
     println!("session initialized with tensor plugins");
 
     let dataset = VectorDataset::CohereSmall100k; // This is one of the smaller datasets.
 
     // Download the source parquet files.
     let dataset_paths = vector_dataset::download(dataset, TrainLayout::Single).await?;
-    let (_id, query_vector) = get_query_vector(dataset_paths.test).await?;
+    let (_id, query_vector) = get_query_vector(dataset_paths.test, &mut ctx).await?;
     println!(
         "query vector selected (id = {_id}, dim = {})",
         query_vector.len()
@@ -142,18 +143,21 @@ async fn main() -> Result<()> {
     verify_roundtrip(&session, &bytes, struct_array.clone()).await?;
 
     println!("verifying filter pushdown with cosine similarity...");
-    verify_filter_pushdown(&session, &bytes, &query_vector, struct_array).await?;
+    verify_filter_pushdown(&session, &bytes, &query_vector, struct_array, &mut ctx).await?;
 
     println!("all checks passed!");
     Ok(())
 }
 
-async fn get_query_vector(query_vectors_path: PathBuf) -> Result<(usize, Vec<f32>)> {
+async fn get_query_vector(
+    query_vectors_path: PathBuf,
+    ctx: &mut ExecutionCtx,
+) -> Result<(usize, Vec<f32>)> {
     let test_vectors = parquet_to_vortex_chunks(query_vectors_path).await?;
 
     // Get a random query vector.
     let idx = rand::random_range(0..test_vectors.len());
-    let struct_scalar = test_vectors.scalar_at(idx)?;
+    let struct_scalar = test_vectors.execute_scalar(idx, ctx)?;
     let id_scalar = struct_scalar
         .as_struct()
         .field("id")
@@ -260,6 +264,7 @@ async fn verify_filter_pushdown(
     bytes: &ByteBuffer,
     query: &[f32],
     original: ArrayRef,
+    ctx: &mut ExecutionCtx,
 ) -> Result<()> {
     // Build the filter as `cosine_similarity(emb, <query>) > threshold`. The RHS of
     // `CosineSimilarity` is a `lit(...)` wrapping a `Vector<f32, DIM>` scalar; during scan
@@ -297,13 +302,12 @@ async fn verify_filter_pushdown(
     // Materialize the matching rows and dump each `emb` vector so the reader can see what the
     // pushed-down filter actually selected. Vectors are truncated to the first few elements since
     // DIM is typically large.
-    let mut ctx = session.create_execution_ctx();
     let filtered: StructArray = ChunkedArray::try_new(chunks, original.dtype().clone())?
         .into_array()
-        .execute(&mut ctx)?;
+        .execute(ctx)?;
 
     let emb = filtered.unmasked_field_by_name("emb")?.clone();
-    let flat = flatten_vector_column(emb, &mut ctx)?;
+    let flat = flatten_vector_column(emb, ctx)?;
 
     let dim = query.len();
     for (i, row) in flat.chunks_exact(dim).enumerate() {