[GitHub] [arrow-datafusion] Ted-Jiang commented on a change in pull request #2031: #2004 approx percentile with weight

[GitBox <gi...@apache.org>]

Ted-Jiang commented on a change in pull request #2031:
URL: https://github.com/apache/arrow-datafusion/pull/2031#discussion_r832880777



##########
File path: datafusion-physical-expr/src/expressions/approx_percentile_cont_with_weight.rs
##########
@@ -0,0 +1,154 @@
+// 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 crate::expressions::approx_percentile_cont::ApproxPercentileAccumulator;
+use crate::expressions::ApproxPercentileCont;
+use crate::{
+    tdigest::{Centroid, TDigest, DEFAULT_MAX_SIZE},
+    AggregateExpr, PhysicalExpr,
+};
+use arrow::{
+    array::ArrayRef,
+    datatypes::{DataType, Field},
+};
+
+use datafusion_common::Result;
+use datafusion_common::ScalarValue;
+use datafusion_expr::Accumulator;
+
+use std::{any::Any, sync::Arc};
+
+/// APPROX_PERCENTILE_CONT_WITH_WEIGTH aggregate expression
+#[derive(Debug)]
+pub struct ApproxPercentileContWithWeight {
+    approx_percentile_cont: ApproxPercentileCont,
+    column_expr: Arc<dyn PhysicalExpr>,
+    weight_expr: Arc<dyn PhysicalExpr>,
+}
+
+impl ApproxPercentileContWithWeight {
+    /// Create a new [`ApproxPercentileContWithWeight`] aggregate function.
+    pub fn new(
+        expr: Vec<Arc<dyn PhysicalExpr>>,
+        name: impl Into<String>,
+        return_type: DataType,
+    ) -> Result<Self> {
+        // Arguments should be [ColumnExpr, WeightExpr, DesiredPercentileLiteral]
+        debug_assert_eq!(expr.len(), 3);
+
+        let sub_expr = vec![expr[0].clone(), expr[2].clone()];
+        let approx_percentile_cont =
+            ApproxPercentileCont::new(sub_expr, name, return_type)?;
+
+        Ok(Self {
+            approx_percentile_cont,
+            column_expr: expr[0].clone(),
+            weight_expr: expr[1].clone(),
+        })
+    }
+}
+
+impl AggregateExpr for ApproxPercentileContWithWeight {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn field(&self) -> Result<Field> {
+        self.approx_percentile_cont.field()
+    }
+
+    #[allow(rustdoc::private_intra_doc_links)]
+    /// See [`TDigest::to_scalar_state()`] for a description of the serialised
+    /// state.
+    fn state_fields(&self) -> Result<Vec<Field>> {
+        self.approx_percentile_cont.state_fields()
+    }
+
+    fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> {
+        vec![self.column_expr.clone(), self.weight_expr.clone()]
+    }
+
+    fn create_accumulator(&self) -> Result<Box<dyn Accumulator>> {
+        let approx_percentile_cont_accumulator =
+            self.approx_percentile_cont.create_plain_accumulator()?;
+        let accumulator = ApproxPercentileWithWeightAccumulator::new(
+            approx_percentile_cont_accumulator,
+        );
+        Ok(Box::new(accumulator))
+    }
+
+    fn name(&self) -> &str {
+        self.approx_percentile_cont.name()
+    }
+}
+
+#[derive(Debug)]
+pub struct ApproxPercentileWithWeightAccumulator {
+    approx_percentile_cont_accumulator: ApproxPercentileAccumulator,
+}
+
+impl ApproxPercentileWithWeightAccumulator {
+    pub fn new(approx_percentile_cont_accumulator: ApproxPercentileAccumulator) -> Self {
+        Self {
+            approx_percentile_cont_accumulator,
+        }
+    }
+}
+
+impl Accumulator for ApproxPercentileWithWeightAccumulator {
+    fn state(&self) -> Result<Vec<ScalarValue>> {
+        self.approx_percentile_cont_accumulator.state()
+    }
+
+    fn update_batch(&mut self, values: &[ArrayRef]) -> Result<()> {
+        debug_assert_eq!(
+            values.len(),
+            2,
+            "invalid number of values in batch percentile update"
+        );
+        let means = &values[0];
+        let weights = &values[1];
+        debug_assert_eq!(
+            means.len(),
+            weights.len(),
+            "invalid number of values in means and weights"
+        );
+        let means_f64 = ApproxPercentileAccumulator::convert_to_ordered_float(means)?;
+        let weights_f64 = ApproxPercentileAccumulator::convert_to_ordered_float(weights)?;
+        let mut digests: Vec<TDigest> = vec![];
+        for (mean, weight) in means_f64.iter().zip(weights_f64.iter()) {
+            digests.push(TDigest::new_with_centroid(
+                DEFAULT_MAX_SIZE,
+                Centroid::new(*mean, *weight),
+            ))
+        }
+        self.approx_percentile_cont_accumulator
+            .merge_digests(&digests);

Review comment:
       IMO, still use `approx_percentile_cont_accumulator.merge_digests`, why not change the struct `[approx_percentile_cont.rs]` to support `weight `. If i miss something plz tell me.




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