## Coverage Report

#### Created: 2024-10-13 08:39

    /Users/andrewlamb/Software/datafusion/datafusion/functions-aggregate/src/approx_median.rs

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    // Licensed to the Apache Software Foundation (ASF) under one
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    // or more contributor license agreements.  See the NOTICE file
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    // distributed with this work for additional information
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    // regarding copyright ownership.  The ASF licenses this file
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    // to you under the Apache License, Version 2.0 (the
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    // "License"); you may not use this file except in compliance
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    // with the License.  You may obtain a copy of the License at
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    //
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    //   http://www.apache.org/licenses/LICENSE-2.0
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    //
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    // Unless required by applicable law or agreed to in writing,
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    // software distributed under the License is distributed on an
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    // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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    // KIND, either express or implied.  See the License for the
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    // specific language governing permissions and limitations
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    // under the License.
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    //! Defines physical expressions for APPROX_MEDIAN that can be evaluated MEDIAN at runtime during query execution
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    use std::any::Any;
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    use std::fmt::Debug;
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    use arrow::{datatypes::DataType, datatypes::Field};
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    use arrow_schema::DataType::{Float64, UInt64};
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    use datafusion_common::{not_impl_err, plan_err, Result};
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    use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
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    use datafusion_expr::type_coercion::aggregates::NUMERICS;
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    use datafusion_expr::utils::format_state_name;
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    use datafusion_expr::{Accumulator, AggregateUDFImpl, Signature, Volatility};
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    use crate::approx_percentile_cont::ApproxPercentileAccumulator;
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    make_udaf_expr_and_func!(
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        ApproxMedian,
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        approx_median,
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        expression,
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        "Computes the approximate median of a set of numbers",
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        approx_median_udaf
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    );
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    /// APPROX_MEDIAN aggregate expression
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    pub struct ApproxMedian {
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        signature: Signature,
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    }
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    impl Debug for ApproxMedian {
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        fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
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            f.debug_struct("ApproxMedian")
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                .field("name", &self.name())
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                .field("signature", &self.signature)
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                .finish()
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        }
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    }
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    impl Default for ApproxMedian {
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        fn default() -> Self {
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            Self::new()
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        }
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    }
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    impl ApproxMedian {
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        /// Create a new APPROX_MEDIAN aggregate function
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        pub fn new() -> Self {
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            Self {
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                signature: Signature::uniform(1, NUMERICS.to_vec(), Volatility::Immutable),
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            }
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        }
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    }
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    impl AggregateUDFImpl for ApproxMedian {
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        /// Return a reference to Any that can be used for downcasting
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        fn as_any(&self) -> &dyn Any {
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            self
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        }
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        fn state_fields(&self, args: StateFieldsArgs) -> Result<Vec<Field>> {
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            Ok(vec![
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                Field::new(format_state_name(args.name, "max_size"), UInt64, false),
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                Field::new(format_state_name(args.name, "sum"), Float64, false),
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                Field::new(format_state_name(args.name, "count"), UInt64, false),
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                Field::new(format_state_name(args.name, "max"), Float64, false),
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                Field::new(format_state_name(args.name, "min"), Float64, false),
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                Field::new_list(
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                    format_state_name(args.name, "centroids"),
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                    Field::new("item", Float64, true),
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                    false,
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                ),
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            ])
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        }
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        fn name(&self) -> &str {
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            "approx_median"
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        }
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        fn signature(&self) -> &Signature {
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            &self.signature
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        }
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        fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
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            if !arg_types[0].is_numeric() {
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                return plan_err!("ApproxMedian requires numeric input types");
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            }
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            Ok(arg_types[0].clone())
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        }
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        fn accumulator(&self, acc_args: AccumulatorArgs) -> Result<Box<dyn Accumulator>> {
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            if acc_args.is_distinct {
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                return not_impl_err!(
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                    "APPROX_MEDIAN(DISTINCT) aggregations are not available"
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                );
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            }
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            Ok(Box::new(ApproxPercentileAccumulator::new(
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                0.5_f64,
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                acc_args.exprs[0].data_type(acc_args.schema)?,
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            )))
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        }
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    }