Fix parquet predicate filtering with column projection

cpp/include/cudf/io/parquet.hpp

@@ -195,6 +195,10 @@ class parquet_reader_options {
   /**
    * @brief Sets AST based filter for predicate pushdown.
    *
+   * The filter can utilize cudf::ast::column_name_reference to reference a column by its name,
+   * even if it's not necessarily present in the requested projected columns.
+   * To refer to output column indices, you can use cudf::ast::column_reference.
+   *
    * @param filter AST expression to use as filter
    */
   void set_filter(ast::expression const& filter) { _filter = filter; }
@@ -292,9 +296,13 @@ class parquet_reader_options_builder {
   }
 
   /**
-   * @brief Sets vector of individual row groups to read.
+   * @brief Sets AST based filter for predicate pushdown.
    *
-   * @param filter Vector of row groups to read
+   * The filter can utilize cudf::ast::column_name_reference to reference a column by its name,
+   * even if it's not necessarily present in the requested projected columns.
+   * To refer to output column indices, you can use cudf::ast::column_reference.
+   *
+   * @param filter AST expression to use as filter
    * @return this for chaining
    */
   parquet_reader_options_builder& filter(ast::expression const& filter)

cpp/tests/io/parquet_reader_test.cpp

@@ -1413,18 +1413,34 @@ TEST_F(ParquetReaderTest, FilterWithColumnProjection)
   auto lit             = cudf::ast::literal{val};
   auto col_ref         = cudf::ast::column_name_reference{"col_uint32"};
   auto col_index       = cudf::ast::column_reference{0};
-  auto read_expr       = cudf::ast::operation(cudf::ast::ast_operator::LESS, col_ref, lit);
   auto filter_expr     = cudf::ast::operation(cudf::ast::ast_operator::LESS, col_index, lit);
 
-  auto predicate       = cudf::compute_column(src, filter_expr);
-  auto projected_table = cudf::table_view{{src.get_column(2)}};
-  auto expected        = cudf::apply_boolean_mask(projected_table, *predicate);
+  auto predicate = cudf::compute_column(src, filter_expr);
 
-  auto read_opts = cudf::io::parquet_reader_options::builder(cudf::io::source_info{filepath})
-                     .columns({"col_double"})
-                     .filter(read_expr);
-  auto result = cudf::io::read_parquet(read_opts);
-  CUDF_TEST_EXPECT_TABLES_EQUAL(*result.tbl, *expected);
+  {  // column_name_reference in parquet filter (not present in column projection)
+    auto read_expr       = cudf::ast::operation(cudf::ast::ast_operator::LESS, col_ref, lit);
+    auto projected_table = cudf::table_view{{src.get_column(2)}};
+    auto expected        = cudf::apply_boolean_mask(projected_table, *predicate);
+
+    auto read_opts = cudf::io::parquet_reader_options::builder(cudf::io::source_info{filepath})
+                       .columns({"col_double"})
+                       .filter(read_expr);
+    auto result = cudf::io::read_parquet(read_opts);
+    CUDF_TEST_EXPECT_TABLES_EQUAL(*result.tbl, *expected);
+  }
+
+  {  // column_reference in parquet filter (indices as per order of column projection)
+    auto col_index2    = cudf::ast::column_reference{1};
+    auto read_ref_expr = cudf::ast::operation(cudf::ast::ast_operator::LESS, col_index, lit);
+
+    auto projected_table = cudf::table_view{{src.get_column(2), src.get_column(0)}};
+    auto expected        = cudf::apply_boolean_mask(projected_table, *predicate);
+    auto read_opts = cudf::io::parquet_reader_options::builder(cudf::io::source_info{filepath})
+                       .columns({"col_double", "col_uint32"})
+                       .filter(read_ref_expr);
+    auto result = cudf::io::read_parquet(read_opts);
+    CUDF_TEST_EXPECT_TABLES_EQUAL(*result.tbl, *expected);
+  }
 }
 
 TEST_F(ParquetReaderTest, FilterReferenceExpression)