Simplified API to get iterator

README.md

@@ -102,7 +102,8 @@ distribute work across threads. E.g.
 ```rust 
 let handles = vec![];
 for column in columns {
-    let compressed_pages = get_page_iterator(&metadata, row_group, column, &mut file, file)?.collect()?;
+    let column_meta = metadata.row_groups[row_group].column(column);
+    let compressed_pages = get_page_iterator(column_meta, &mut file, file)?.collect()?;
     // each compressed_page has a buffer; cloning is expensive(!). We move it so that the memory
     // is released at the end of the processing.
     handles.push(thread::spawn move {

examples/s3/src/main.rs

@@ -49,9 +49,11 @@ async fn main() -> Result<()> {
 
     // * first row group
     // * first column
+    let column_metadata = metadata.row_groups[row_group].column(column);
+
     // * do not skip any pages
     let pages =
-        get_page_stream(&metadata, 0, 0, &mut reader, vec![], Arc::new(|_, _| true)).await?;
+        get_page_stream(&column_metadata, &mut reader, vec![], Arc::new(|_, _| true)).await?;
 
     pin_mut!(pages); // needed for iteration
 

integration-tests/src/read/mod.rs

@@ -97,20 +97,15 @@ pub(crate) mod tests {
         column: usize,
     ) -> Result<(Array, Option<std::sync::Arc<dyn Statistics>>)> {
         let metadata = read_metadata(reader)?;
-        let descriptor = metadata.row_groups[row_group]
-            .column(column)
-            .descriptor()
-            .clone();
+        let column_meta = metadata.row_groups[row_group].column(column);
+        let descriptor = column_meta.descriptor().clone();
 
-        let iterator = get_page_iterator(&metadata, row_group, column, reader, None, vec![])?;
+        let iterator = get_page_iterator(&column_meta, reader, None, vec![])?;
 
         let buffer = vec![];
         let mut iterator = Decompressor::new(iterator, buffer);
 
-        let statistics = metadata.row_groups[row_group]
-            .column(column)
-            .statistics()
-            .transpose()?;
+        let statistics = column_meta.statistics().transpose()?;
 
         let page = iterator.next().unwrap().as_ref().unwrap();
 

parquet-tools/src/lib/dump.rs

@@ -47,7 +47,8 @@ where
         writeln!(writer, "{}", SEPARATOR)?;
 
         for column in &columns {
-            let iter = get_page_iterator(&metadata, i, *column, &mut file)?;
+            let column_meta = group.column(column);
+            let iter = get_page_iterator(column_meta, &mut file)?;
             for (page_ind, page) in iter.enumerate() {
                 let page = page?;
                 writeln!(

src/read/mod.rs

@@ -19,7 +19,7 @@ pub use stream::read_metadata as read_metadata_async;
 use std::io::{Read, Seek, SeekFrom};
 use std::sync::Arc;
 
-use crate::metadata::RowGroupMetaData;
+use crate::metadata::{ColumnChunkMetaData, RowGroupMetaData};
 use crate::{error::Result, metadata::FileMetaData};
 
 pub use page_iterator::{PageFilter, PageIterator};
@@ -44,16 +44,13 @@ pub fn filter_row_groups(
 }
 
 pub fn get_page_iterator<'a, RR: Read + Seek>(
-    metadata: &FileMetaData,
-    row_group: usize,
-    column: usize,
+    column_metadata: &ColumnChunkMetaData,
     reader: &'a mut RR,
     pages_filter: Option<PageFilter>,
     buffer: Vec<u8>,
 ) -> Result<PageIterator<'a, RR>> {
     let pages_filter = pages_filter.unwrap_or_else(|| Arc::new(|_, _| true));
 
-    let column_metadata = metadata.row_groups[row_group].column(column);
     let (col_start, _) = column_metadata.byte_range();
     reader.seek(SeekFrom::Start(col_start))?;
     Ok(PageIterator::new(
@@ -84,8 +81,9 @@ mod tests {
 
         let row_group = 0;
         let column = 0;
+        let column_metadata = metadata.row_groups[row_group].column(column);
         let buffer = vec![];
-        let mut iter = get_page_iterator(&metadata, row_group, column, &mut file, None, buffer)?;
+        let mut iter = get_page_iterator(column_metadata, &mut file, None, buffer)?;
 
         let page = iter.next().unwrap().unwrap();
         assert_eq!(page.num_values(), 8);
@@ -102,9 +100,9 @@ mod tests {
 
         let row_group = 0;
         let column = 0;
+        let column_metadata = metadata.row_groups[row_group].column(column);
         let buffer = vec![0];
-        let mut iterator =
-            get_page_iterator(&metadata, row_group, column, &mut file, None, buffer)?;
+        let mut iterator = get_page_iterator(column_metadata, &mut file, None, buffer)?;
 
         let page = iterator.next().unwrap().unwrap();
         iterator.reuse_buffer(page.buffer);
@@ -125,8 +123,9 @@ mod tests {
 
         let row_group = 0;
         let column = 0;
+        let column_metadata = metadata.row_groups[row_group].column(column);
         let buffer = vec![1];
-        let iterator = get_page_iterator(&metadata, row_group, column, &mut file, None, buffer)?;
+        let iterator = get_page_iterator(column_metadata, &mut file, None, buffer)?;
 
         let buffer = vec![];
         let mut iterator = Decompressor::new(iterator, buffer);

src/read/page_stream.rs

@@ -6,22 +6,19 @@ use parquet_format_async_temp::thrift::protocol::TCompactInputStreamProtocol;
 
 use crate::compression::Compression;
 use crate::error::Result;
-use crate::metadata::{ColumnDescriptor, FileMetaData};
+use crate::metadata::{ColumnChunkMetaData, ColumnDescriptor};
 use crate::page::{CompressedDataPage, ParquetPageHeader};
 
 use super::page_iterator::{finish_page, get_page_header, FinishedPage};
 use super::PageFilter;
 
 /// Returns a stream of compressed data pages
 pub async fn get_page_stream<'a, RR: AsyncRead + Unpin + Send + AsyncSeek>(
-    metadata: &'a FileMetaData,
-    row_group: usize,
-    column: usize,
+    column_metadata: &'a ColumnChunkMetaData,
     reader: &'a mut RR,
     buffer: Vec<u8>,
     pages_filter: PageFilter,
 ) -> Result<impl Stream<Item = Result<CompressedDataPage>> + 'a> {
-    let column_metadata = metadata.row_groups[row_group].column(column);
     let (col_start, _) = column_metadata.byte_range();
     reader.seek(SeekFrom::Start(col_start)).await?;
     Ok(_get_page_stream(