Revert "reorder record batch"

This reverts commit 66d7c4a.

crates/iceberg/src/arrow/reader.rs

@@ -202,8 +202,7 @@ impl ArrowReader {
 
         // Create a projection mask for the batch stream to select which columns in the
         // Parquet file that we want in the response
-        // Since Parquet projection mask will lose the order of the columns, we need to reorder.
-        let (projection_mask, reorder) = Self::get_arrow_projection_mask(
+        let projection_mask = Self::get_arrow_projection_mask(
             &task.project_field_ids,
             &task.schema,
             record_batch_stream_builder.parquet_schema(),
@@ -271,11 +270,6 @@ impl ArrowReader {
         let mut record_batch_stream = record_batch_stream_builder.build()?;
 
         while let Some(batch) = record_batch_stream.try_next().await? {
-            let batch = if let Some(reorder) = reorder.as_ref() {
-                batch.project(&reorder).expect("must be able to reorder")
-            } else {
-                batch
-            };
             tx.send(record_batch_transformer.process_record_batch(batch))
                 .await?
         }
@@ -304,9 +298,9 @@ impl ArrowReader {
         iceberg_schema_of_task: &Schema,
         parquet_schema: &SchemaDescriptor,
         arrow_schema: &ArrowSchemaRef,
-    ) -> Result<(ProjectionMask, Option<Vec<usize>>)> {
+    ) -> Result<ProjectionMask> {
         if field_ids.is_empty() {
-            Ok((ProjectionMask::all(), None))
+            Ok(ProjectionMask::all())
         } else {
             // Build the map between field id and column index in Parquet schema.
             let mut column_map = HashMap::new();
@@ -364,20 +358,7 @@ impl ArrowReader {
                     ));
                 }
             }
-
-            // projection mask is order by indices
-            let mut mask_indices = indices.clone();
-            mask_indices.sort_by_key(|&x| x);
-            // try to reorder the mask_indices to indices
-            let reorder = indices
-                .iter()
-                .map(|idx| mask_indices.iter().position(|&i| i == *idx).unwrap())
-                .collect::<Vec<_>>();
-
-            Ok((
-                ProjectionMask::roots(parquet_schema, indices),
-                Some(reorder),
-            ))
+            Ok(ProjectionMask::roots(parquet_schema, indices))
         }
     }