alamb commented on code in PR #9115:
URL: https://github.com/apache/arrow-rs/pull/9115#discussion_r2679491699
##########
parquet/src/arrow/arrow_reader/mod.rs:
##########
@@ -304,6 +304,36 @@ impl<T> ArrowReaderBuilder<T> {
///
/// It is recommended to enable reading the page index if using this
functionality, to allow
/// more efficient skipping over data pages. See
[`ArrowReaderOptions::with_page_index`].
+ ///
+ /// For a running example see `parquet/examples/read_with_row_filter.rs`.
+ /// See
<https://arrow.apache.org/blog/2025/12/11/parquet-late-materialization-deep-dive/>
Review Comment:
+1
##########
parquet/src/arrow/arrow_reader/mod.rs:
##########
@@ -304,6 +304,36 @@ impl<T> ArrowReaderBuilder<T> {
///
/// It is recommended to enable reading the page index if using this
functionality, to allow
/// more efficient skipping over data pages. See
[`ArrowReaderOptions::with_page_index`].
+ ///
+ /// For a running example see `parquet/examples/read_with_row_filter.rs`.
+ /// See
<https://arrow.apache.org/blog/2025/12/11/parquet-late-materialization-deep-dive/>
+ /// for a technical explanation of late materialization.
+ ///
+ /// # Example
+ /// ```rust
+ /// # use std::fs::File;
+ /// # use arrow_array::Int32Array;
+ /// # use parquet::arrow::ProjectionMask;
+ /// # use parquet::arrow::arrow_reader::{ArrowPredicateFn,
ParquetRecordBatchReaderBuilder, RowFilter};
+ /// # fn main() -> Result<(), parquet::errors::ParquetError> {
+ /// # let testdata = arrow::util::test_util::parquet_test_data();
+ /// # let path = format!("{testdata}/alltypes_plain.parquet");
+ /// # let file = File::open(&path)?;
+ /// let builder = ParquetRecordBatchReaderBuilder::try_new(file)?;
+ /// let schema_desc =
builder.metadata().file_metadata().schema_descr_ptr();
+ ///
+ /// // Create predicate: column id > 4. This col has index 0.
+ /// let projection = ProjectionMask::leaves(&schema_desc, [0]);
+ /// let predicate = ArrowPredicateFn::new(projection, |batch| {
+ /// let id_col = batch.column(0);
Review Comment:
As a minor suggestion, I think it would make a nicer example if you picked a
different column from the file other than 0 so that it is clear the batch
passed to the predicate only contains the selected projection column
For example, perhaps you could use the `int_col` (column index 4)
```sql
> select * from './parquet-testing/data/alltypes_plain.parquet';
+----+----------+-------------+--------------+---------+------------+-----------+------------+------------------+------------+---------------------+
| id | bool_col | tinyint_col | smallint_col | int_col | bigint_col |
float_col | double_col | date_string_col | string_col | timestamp_col |
+----+----------+-------------+--------------+---------+------------+-----------+------------+------------------+------------+---------------------+
| 4 | true | 0 | 0 | 0 | 0 | 0.0
| 0.0 | 30332f30312f3039 | 30 | 2009-03-01T00:00:00 |
| 5 | false | 1 | 1 | 1 | 10 | 1.1
| 10.1 | 30332f30312f3039 | 31 | 2009-03-01T00:01:00 |
| 6 | true | 0 | 0 | 0 | 0 | 0.0
| 0.0 | 30342f30312f3039 | 30 | 2009-04-01T00:00:00 |
| 7 | false | 1 | 1 | 1 | 10 | 1.1
| 10.1 | 30342f30312f3039 | 31 | 2009-04-01T00:01:00 |
| 2 | true | 0 | 0 | 0 | 0 | 0.0
| 0.0 | 30322f30312f3039 | 30 | 2009-02-01T00:00:00 |
| 3 | false | 1 | 1 | 1 | 10 | 1.1
| 10.1 | 30322f30312f3039 | 31 | 2009-02-01T00:01:00 |
| 0 | true | 0 | 0 | 0 | 0 | 0.0
| 0.0 | 30312f30312f3039 | 30 | 2009-01-01T00:00:00 |
| 1 | false | 1 | 1 | 1 | 10 | 1.1
| 10.1 | 30312f30312f3039 | 31 | 2009-01-01T00:01:00 |
+----+----------+-------------+--------------+---------+------------+-----------+------------+------------------+------------+---------------------+
8 row(s) fetched.
Elapsed 0.039 seconds.
> describe './parquet-testing/data/alltypes_plain.parquet';
+-----------------+---------------+-------------+
| column_name | data_type | is_nullable |
+-----------------+---------------+-------------+
| id | Int32 | YES |
| bool_col | Boolean | YES |
| tinyint_col | Int32 | YES |
| smallint_col | Int32 | YES |
| int_col | Int32 | YES |
| bigint_col | Int64 | YES |
| float_col | Float32 | YES |
| double_col | Float64 | YES |
| date_string_col | BinaryView | YES |
| string_col | BinaryView | YES |
| timestamp_col | Timestamp(ns) | YES |
+-----------------+---------------+-------------+
11 row(s) fetched.
Elapsed 0.005 seconds.
```
##########
parquet/examples/read_with_row_filter.rs:
##########
@@ -0,0 +1,49 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use arrow_array::Int32Array;
+use arrow_cast::pretty::print_batches;
+use parquet::arrow::ProjectionMask;
+use parquet::arrow::arrow_reader::{ArrowPredicateFn,
ParquetRecordBatchReaderBuilder, RowFilter};
+use parquet::errors::Result;
+use std::fs::File;
+
+// RowFilter / with_row_filter usage. For background and more
Review Comment:
Yes, I agree -- I think the doc examples are easier to find so I recommend
removing this example file
Actually, looking at the existing examples I think many of them are
redundant / would be easier to find if we moved them into the documentation:
https://github.com/apache/arrow-rs/tree/main/parquet/examples
##########
parquet/src/arrow/arrow_reader/mod.rs:
##########
@@ -304,6 +304,36 @@ impl<T> ArrowReaderBuilder<T> {
///
/// It is recommended to enable reading the page index if using this
functionality, to allow
/// more efficient skipping over data pages. See
[`ArrowReaderOptions::with_page_index`].
+ ///
+ /// For a running example see `parquet/examples/read_with_row_filter.rs`.
+ /// See
<https://arrow.apache.org/blog/2025/12/11/parquet-late-materialization-deep-dive/>
+ /// for a technical explanation of late materialization.
+ ///
+ /// # Example
+ /// ```rust
+ /// # use std::fs::File;
+ /// # use arrow_array::Int32Array;
+ /// # use parquet::arrow::ProjectionMask;
+ /// # use parquet::arrow::arrow_reader::{ArrowPredicateFn,
ParquetRecordBatchReaderBuilder, RowFilter};
+ /// # fn main() -> Result<(), parquet::errors::ParquetError> {
+ /// # let testdata = arrow::util::test_util::parquet_test_data();
+ /// # let path = format!("{testdata}/alltypes_plain.parquet");
+ /// # let file = File::open(&path)?;
+ /// let builder = ParquetRecordBatchReaderBuilder::try_new(file)?;
+ /// let schema_desc =
builder.metadata().file_metadata().schema_descr_ptr();
+ ///
+ /// // Create predicate: column id > 4. This col has index 0.
Review Comment:
```suggestion
/// // Create predicate that evaluates `id > 4`. The `id` column has
index 0.
```
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