datafusion_functions/math/
signum.rs

// 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 std::any::Any;
use std::sync::{Arc, OnceLock};

use arrow::array::{ArrayRef, AsArray};
use arrow::datatypes::DataType::{Float32, Float64};
use arrow::datatypes::{DataType, Float32Type, Float64Type};

use datafusion_common::{exec_err, Result};
use datafusion_expr::scalar_doc_sections::DOC_SECTION_MATH;
use datafusion_expr::sort_properties::{ExprProperties, SortProperties};
use datafusion_expr::{
    ColumnarValue, Documentation, ScalarUDFImpl, Signature, Volatility,
};

use crate::utils::make_scalar_function;

#[derive(Debug)]
pub struct SignumFunc {
    signature: Signature,
}

impl Default for SignumFunc {
    fn default() -> Self {
        SignumFunc::new()
    }
}

impl SignumFunc {
    pub fn new() -> Self {
        use DataType::*;
        Self {
            signature: Signature::uniform(
                1,
                vec![Float64, Float32],
                Volatility::Immutable,
            ),
        }
    }
}

impl ScalarUDFImpl for SignumFunc {
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn name(&self) -> &str {
        "signum"
    }

    fn signature(&self) -> &Signature {
        &self.signature
    }

    fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
        match &arg_types[0] {
            Float32 => Ok(Float32),
            _ => Ok(Float64),
        }
    }

    fn output_ordering(&self, input: &[ExprProperties]) -> Result<SortProperties> {
        // Non-decreasing for all real numbers x.
        Ok(input[0].sort_properties)
    }

    fn invoke(&self, args: &[ColumnarValue]) -> Result<ColumnarValue> {
        make_scalar_function(signum, vec![])(args)
    }

    fn documentation(&self) -> Option<&Documentation> {
        Some(get_signum_doc())
    }
}

static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();

fn get_signum_doc() -> &'static Documentation {
    DOCUMENTATION.get_or_init(|| {
        Documentation::builder()
            .with_doc_section(DOC_SECTION_MATH)
            .with_description(
                r#"Returns the sign of a number.
Negative numbers return `-1`.
Zero and positive numbers return `1`."#,
            )
            .with_syntax_example("signum(numeric_expression)")
            .with_standard_argument("numeric_expression", Some("Numeric"))
            .build()
            .unwrap()
    })
}

/// signum SQL function
pub fn signum(args: &[ArrayRef]) -> Result<ArrayRef> {
    match args[0].data_type() {
        Float64 => Ok(Arc::new(
            args[0]
                .as_primitive::<Float64Type>()
                .unary::<_, Float64Type>(
                    |x: f64| {
                        if x == 0_f64 {
                            0_f64
                        } else {
                            x.signum()
                        }
                    },
                ),
        ) as ArrayRef),

        Float32 => Ok(Arc::new(
            args[0]
                .as_primitive::<Float32Type>()
                .unary::<_, Float32Type>(
                    |x: f32| {
                        if x == 0_f32 {
                            0_f32
                        } else {
                            x.signum()
                        }
                    },
                ),
        ) as ArrayRef),

        other => exec_err!("Unsupported data type {other:?} for function signum"),
    }
}

#[cfg(test)]
mod test {
    use std::sync::Arc;

    use arrow::array::{Float32Array, Float64Array};

    use datafusion_common::cast::{as_float32_array, as_float64_array};
    use datafusion_expr::{ColumnarValue, ScalarUDFImpl};

    use crate::math::signum::SignumFunc;

    #[test]
    fn test_signum_f32() {
        let array = Arc::new(Float32Array::from(vec![
            -1.0,
            -0.0,
            0.0,
            1.0,
            -0.01,
            0.01,
            f32::NAN,
            f32::INFINITY,
            f32::NEG_INFINITY,
        ]));
        let batch_size = array.len();
        let result = SignumFunc::new()
            .invoke_batch(&[ColumnarValue::Array(array)], batch_size)
            .expect("failed to initialize function signum");

        match result {
            ColumnarValue::Array(arr) => {
                let floats = as_float32_array(&arr)
                    .expect("failed to convert result to a Float32Array");

                assert_eq!(floats.len(), 9);
                assert_eq!(floats.value(0), -1.0);
                assert_eq!(floats.value(1), 0.0);
                assert_eq!(floats.value(2), 0.0);
                assert_eq!(floats.value(3), 1.0);
                assert_eq!(floats.value(4), -1.0);
                assert_eq!(floats.value(5), 1.0);
                assert!(floats.value(6).is_nan());
                assert_eq!(floats.value(7), 1.0);
                assert_eq!(floats.value(8), -1.0);
            }
            ColumnarValue::Scalar(_) => {
                panic!("Expected an array value")
            }
        }
    }

    #[test]
    fn test_signum_f64() {
        let array = Arc::new(Float64Array::from(vec![
            -1.0,
            -0.0,
            0.0,
            1.0,
            -0.01,
            0.01,
            f64::NAN,
            f64::INFINITY,
            f64::NEG_INFINITY,
        ]));
        let batch_size = array.len();
        let result = SignumFunc::new()
            .invoke_batch(&[ColumnarValue::Array(array)], batch_size)
            .expect("failed to initialize function signum");

        match result {
            ColumnarValue::Array(arr) => {
                let floats = as_float64_array(&arr)
                    .expect("failed to convert result to a Float32Array");

                assert_eq!(floats.len(), 9);
                assert_eq!(floats.value(0), -1.0);
                assert_eq!(floats.value(1), 0.0);
                assert_eq!(floats.value(2), 0.0);
                assert_eq!(floats.value(3), 1.0);
                assert_eq!(floats.value(4), -1.0);
                assert_eq!(floats.value(5), 1.0);
                assert!(floats.value(6).is_nan());
                assert_eq!(floats.value(7), 1.0);
                assert_eq!(floats.value(8), -1.0);
            }
            ColumnarValue::Scalar(_) => {
                panic!("Expected an array value")
            }
        }
    }
}
datafusion_functions/math/signum.rs

datafusion_functions/math/
signum.rs
