datafusion_functions_nested/
cardinality.rs

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// distributed with this work for additional information
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// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
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//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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// specific language governing permissions and limitations
// under the License.

//! [`ScalarUDFImpl`] definitions for cardinality function.

use crate::utils::make_scalar_function;
use arrow_array::{
    Array, ArrayRef, GenericListArray, MapArray, OffsetSizeTrait, UInt64Array,
};
use arrow_schema::DataType;
use arrow_schema::DataType::{FixedSizeList, LargeList, List, Map, UInt64};
use datafusion_common::cast::{as_large_list_array, as_list_array, as_map_array};
use datafusion_common::Result;
use datafusion_common::{exec_err, plan_err};
use datafusion_expr::scalar_doc_sections::DOC_SECTION_ARRAY;
use datafusion_expr::{
    ArrayFunctionSignature, ColumnarValue, Documentation, ScalarUDFImpl, Signature,
    TypeSignature, Volatility,
};
use std::any::Any;
use std::sync::{Arc, OnceLock};

make_udf_expr_and_func!(
    Cardinality,
    cardinality,
    array,
    "returns the total number of elements in the array or map.",
    cardinality_udf
);

impl Cardinality {
    pub fn new() -> Self {
        Self {
            signature: Signature::one_of(
                vec![
                    TypeSignature::ArraySignature(ArrayFunctionSignature::Array),
                    TypeSignature::ArraySignature(ArrayFunctionSignature::MapArray),
                ],
                Volatility::Immutable,
            ),
            aliases: vec![],
        }
    }
}

#[derive(Debug)]
pub(super) struct Cardinality {
    signature: Signature,
    aliases: Vec<String>,
}
impl ScalarUDFImpl for Cardinality {
    fn as_any(&self) -> &dyn Any {
        self
    }
    fn name(&self) -> &str {
        "cardinality"
    }

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

    fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
        Ok(match arg_types[0] {
            List(_) | LargeList(_) | FixedSizeList(_, _) | Map(_, _) => UInt64,
            _ => {
                return plan_err!("The cardinality function can only accept List/LargeList/FixedSizeList/Map.");
            }
        })
    }

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

    fn aliases(&self) -> &[String] {
        &self.aliases
    }

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

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

fn get_cardinality_doc() -> &'static Documentation {
    DOCUMENTATION.get_or_init(|| {
        Documentation::builder()
            .with_doc_section(DOC_SECTION_ARRAY)
            .with_description(
                "Returns the total number of elements in the array.",
            )
            .with_syntax_example("cardinality(array)")
            .with_sql_example(
                r#"```sql
> select cardinality([[1, 2, 3, 4], [5, 6, 7, 8]]);
+--------------------------------------+
| cardinality(List([1,2,3,4,5,6,7,8])) |
+--------------------------------------+
| 8                                    |
+--------------------------------------+
```"#,
            )
            .with_argument(
                "array",
                "Array expression. Can be a constant, column, or function, and any combination of array operators.",
            )
            .build()
            .unwrap()
    })
}

/// Cardinality SQL function
pub fn cardinality_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
    if args.len() != 1 {
        return exec_err!("cardinality expects one argument");
    }

    match &args[0].data_type() {
        List(_) => {
            let list_array = as_list_array(&args[0])?;
            generic_list_cardinality::<i32>(list_array)
        }
        LargeList(_) => {
            let list_array = as_large_list_array(&args[0])?;
            generic_list_cardinality::<i64>(list_array)
        }
        Map(_, _) => {
            let map_array = as_map_array(&args[0])?;
            generic_map_cardinality(map_array)
        }
        other => {
            exec_err!("cardinality does not support type '{:?}'", other)
        }
    }
}

fn generic_map_cardinality(array: &MapArray) -> Result<ArrayRef> {
    let result: UInt64Array = array
        .iter()
        .map(|opt_arr| opt_arr.map(|arr| arr.len() as u64))
        .collect();
    Ok(Arc::new(result))
}

fn generic_list_cardinality<O: OffsetSizeTrait>(
    array: &GenericListArray<O>,
) -> Result<ArrayRef> {
    let result = array
        .iter()
        .map(|arr| match crate::utils::compute_array_dims(arr)? {
            Some(vector) => Ok(Some(vector.iter().map(|x| x.unwrap()).product::<u64>())),
            None => Ok(None),
        })
        .collect::<Result<UInt64Array>>()?;
    Ok(Arc::new(result) as ArrayRef)
}
datafusion_functions_nested/cardinality.rs

datafusion_functions_nested/
cardinality.rs
