vegarsti commented on code in PR #17837:
URL: https://github.com/apache/datafusion/pull/17837#discussion_r2394582337
##########
datafusion/functions-aggregate/src/string_agg.rs:
##########
@@ -269,6 +301,103 @@ fn filter_index<T: Clone>(values: &[T], index: usize) ->
Vec<T> {
.collect::<Vec<_>>()
}
+/// StringAgg accumulator for the simple case (no order or distinct specified)
+/// This accumulator is more efficient than `StringAggAccumulator`
+#[derive(Debug)]
+pub(crate) struct SimpleStringAggAccumulator {
+ delimiter: String,
+ // Updating during `update_batch()`. e.g. "foo,bar"
+ in_progress_string: String,
+ has_value: bool,
+}
+
+impl SimpleStringAggAccumulator {
+ pub fn new(delimiter: &str) -> Self {
+ Self {
+ delimiter: delimiter.to_string(),
+ in_progress_string: "".to_string(),
+ has_value: false,
+ }
+ }
+
+ #[inline]
+ fn append_strings<'a, I>(&mut self, iter: I)
+ where
+ I: Iterator<Item = Option<&'a str>>,
+ {
+ for value in iter.flatten() {
+ if self.has_value {
+ self.in_progress_string.push_str(&self.delimiter);
+ }
+
+ self.in_progress_string.push_str(value);
+ self.has_value = true;
+ }
+ }
+}
+
+impl Accumulator for SimpleStringAggAccumulator {
+ fn update_batch(&mut self, values: &[ArrayRef]) -> Result<()> {
+ let string_arr = values.first().ok_or_else(|| {
+ internal_datafusion_err!(
+ "Planner should ensure its first arg is Utf8/Utf8View"
+ )
+ })?;
+
+ match string_arr.data_type() {
+ DataType::Utf8 => {
+ let array = as_string_array(string_arr)?;
+ self.append_strings(array.iter());
+ }
+ DataType::LargeUtf8 => {
+ let array = as_generic_string_array::<i64>(string_arr)?;
+ self.append_strings(array.iter());
+ }
+ DataType::Utf8View => {
+ let array = as_string_view_array(string_arr)?;
+ self.append_strings(array.iter());
+ }
+ other => {
+ return internal_err!(
+ "Planner should ensure string_agg first argument is
Utf8-like, found {other}"
+ );
+ }
+ }
+
+ Ok(())
+ }
+
+ fn evaluate(&mut self) -> Result<ScalarValue> {
+ let result = if self.has_value {
+ ScalarValue::LargeUtf8(Some(std::mem::take(&mut
self.in_progress_string)))
+ } else {
+ ScalarValue::LargeUtf8(None)
+ };
+
+ self.has_value = false;
+ Ok(result)
+ }
+
+ fn size(&self) -> usize {
+ size_of_val(self) + self.delimiter.capacity() +
self.in_progress_string.capacity()
+ }
+
+ fn state(&mut self) -> Result<Vec<ScalarValue>> {
Review Comment:
Thanks for the explanation! And oh yeah, I should read the doc comments on
the trait!
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