jayzhan211 commented on code in PR #15432:
URL: https://github.com/apache/datafusion/pull/15432#discussion_r2016070941
##########
datafusion/core/src/datasource/statistics.rs:
##########
@@ -145,7 +147,142 @@ pub async fn get_statistics_with_limit(
Ok((result_files, statistics))
}
-fn add_row_stats(
+/// Generic function to compute statistics across multiple items that have
statistics
+fn compute_summary_statistics<T, I>(
+ items: I,
+ file_schema: &SchemaRef,
+ stats_extractor: impl Fn(&T) -> Option<&Statistics>,
+) -> Statistics
+where
+ I: IntoIterator<Item = T>,
+{
+ let size = file_schema.fields().len();
+ let mut col_stats_set = vec![ColumnStatistics::default(); size];
+ let mut num_rows = Precision::<usize>::Absent;
+ let mut total_byte_size = Precision::<usize>::Absent;
+
+ for (idx, item) in items.into_iter().enumerate() {
+ if let Some(item_stats) = stats_extractor(&item) {
+ if idx == 0 {
+ // First item, set values directly
+ num_rows = item_stats.num_rows;
+ total_byte_size = item_stats.total_byte_size;
+ for (index, column_stats) in
+ item_stats.column_statistics.iter().enumerate()
+ {
+ col_stats_set[index].null_count = column_stats.null_count;
+ col_stats_set[index].max_value =
column_stats.max_value.clone();
+ col_stats_set[index].min_value =
column_stats.min_value.clone();
+ col_stats_set[index].sum_value =
column_stats.sum_value.clone();
+ }
+ continue;
+ }
+
+ // Accumulate statistics for subsequent items
+ num_rows = add_row_stats(item_stats.num_rows, num_rows);
+ total_byte_size = add_row_stats(item_stats.total_byte_size,
total_byte_size);
+
+ for (item_col_stats, col_stats) in item_stats
+ .column_statistics
+ .iter()
+ .zip(col_stats_set.iter_mut())
+ {
+ col_stats.null_count =
+ add_row_stats(item_col_stats.null_count,
col_stats.null_count);
+ set_max_if_greater(&item_col_stats.max_value, &mut
col_stats.max_value);
+ set_min_if_lesser(&item_col_stats.min_value, &mut
col_stats.min_value);
+ col_stats.sum_value =
item_col_stats.sum_value.add(&col_stats.sum_value);
+ }
+ }
+ }
+
+ Statistics {
+ num_rows,
+ total_byte_size,
+ column_statistics: col_stats_set,
+ }
+}
+
+/// Computes the summary statistics for a group of files(`FileGroup` level's
statistics).
+///
+/// This function combines statistics from all files in the file group to
create
+/// summary statistics. It handles the following aspects:
+/// - Merges row counts and byte sizes across files
+/// - Computes column-level statistics like min/max values
+/// - Maintains appropriate precision information (exact, inexact, absent)
+///
+/// # Parameters
+/// * `file_group` - The group of files to process
+/// * `file_schema` - Schema of the files
+/// * `collect_stats` - Whether to collect statistics (if false, returns
original file group)
+///
+/// # Returns
+/// A new file group with summary statistics attached
+pub fn compute_file_group_statistics(
+ file_group: FileGroup,
+ file_schema: SchemaRef,
+ collect_stats: bool,
+) -> Result<FileGroup> {
+ if !collect_stats {
+ return Ok(file_group);
+ }
+
+ let statistics =
+ compute_summary_statistics(file_group.iter(), &file_schema, |file| {
+ file.statistics.as_ref().map(|stats| stats.as_ref())
+ });
+
+ Ok(file_group.with_statistics(statistics))
+}
+
+/// Computes statistics for all files across multiple file groups.
+///
+/// This function:
+/// 1. Computes statistics for each individual file group
+/// 2. Summary statistics across all file groups
+/// 3. Optionally marks statistics as inexact
+///
+/// # Parameters
+/// * `file_groups` - Vector of file groups to process
+/// * `file_schema` - Schema of the files
+/// * `collect_stats` - Whether to collect statistics
+/// * `inexact_stats` - Whether to mark the resulting statistics as inexact
+///
+/// # Returns
+/// A tuple containing:
+/// * The processed file groups with their individual statistics attached
+/// * The summary statistics across all file groups, aka all files summary
statistics
+pub fn compute_all_files_statistics(
+ file_groups: Vec<FileGroup>,
+ file_schema: SchemaRef,
+ collect_stats: bool,
+ inexact_stats: bool,
+) -> Result<(Vec<FileGroup>, Statistics)> {
Review Comment:
Why FileGroups? These two are now separated, even though Statistics is still
associated with `Vec<FileGroup>`, so we might compute with the incorrect
`Statistics` easily. Although this is not a major issue.
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