Improve comparison docs and re-export the array-comparing function

src/compute/comparison/binary.rs

@@ -121,6 +121,13 @@ fn gt_eq_scalar<O: Offset>(lhs: &BinaryArray<O>, rhs: &[u8]) -> BooleanArray {
     compare_op_scalar(lhs, rhs, |a, b| a >= b)
 }
 
+/// Compare two [`BinaryArray`]s using the given [`Operator`].
+///
+/// # Errors
+/// When the two arrays have different lengths.
+///
+/// Check the [crate::compute::comparison](module documentation) for usage
+/// examples.
 pub fn compare<O: Offset>(
     lhs: &BinaryArray<O>,
     rhs: &BinaryArray<O>,
@@ -136,6 +143,11 @@ pub fn compare<O: Offset>(
     }
 }
 
+/// Compare a [`BinaryArray`] and a scalar value using the given
+/// [`Operator`].
+///
+/// Check the [crate::compute::comparison](module documentation) for usage
+/// examples.
 pub fn compare_scalar<O: Offset>(
     lhs: &BinaryArray<O>,
     rhs: &BinaryScalar<O>,

src/compute/comparison/boolean.rs

@@ -140,6 +140,13 @@ pub fn gt_eq_scalar(lhs: &BooleanArray, rhs: bool) -> BooleanArray {
     compare_op_scalar(lhs, rhs, |a, b| a | !b)
 }
 
+/// Compare two [`BooleanArray`]s using the given [`Operator`].
+///
+/// # Errors
+/// When the two arrays have different lengths.
+///
+/// Check the [crate::compute::comparison](module documentation) for usage
+/// examples.
 pub fn compare(lhs: &BooleanArray, rhs: &BooleanArray, op: Operator) -> Result<BooleanArray> {
     match op {
         Operator::Eq => eq(lhs, rhs),
@@ -151,6 +158,11 @@ pub fn compare(lhs: &BooleanArray, rhs: &BooleanArray, op: Operator) -> Result<B
     }
 }
 
+/// Compare a [`BooleanArray`] and a scalar value using the given
+/// [`Operator`].
+///
+/// Check the [crate::compute::comparison](module documentation) for usage
+/// examples.
 pub fn compare_scalar(lhs: &BooleanArray, rhs: &BooleanScalar, op: Operator) -> BooleanArray {
     if !rhs.is_valid() {
         return BooleanArray::new_null(DataType::Boolean, lhs.len());

src/compute/comparison/mod.rs

@@ -15,7 +15,67 @@
 // specific language governing permissions and limitations
 // under the License.
 
-//! Defines basic comparison kernels.
+//! Basic comparison kernels.
+//!
+//! The module contains functions that compare either an array and a scalar
+//! or two arrays of the same [`DataType`]. The scalar-oriented functions are
+//! suffixed with `_scalar`. In general, these comparison functions receive as
+//! inputs the two items for comparison and an [`Operator`] which specifies the
+//! type of comparison that will be conducted, such as `<=` ([`Operator::LtEq`]).
+//!
+//! Much like the parent module [`crate::compute`](compute), the comparison functions
+//! have two variants - a statically typed one ([`primitive_compare`])
+//! which expects concrete types such as [`Int8Array`] and a dynamically typed
+//! variant ([`compare`]) that compares values of type `&dyn Array` and errors
+//! if the underlying concrete types mismsatch. The statically-typed functions
+//! are appropriately prefixed with the concrete types they expect.
+//!
+//! Also note that the scalar-based comparison functions for the concrete types,
+//! like [`primitive_compare_scalar`], are infallible and always return a
+//! [`BooleanArray`] while the rest of the functions always wrap the returned
+//! array in a [`Result`] due to their internal checks of the data types and
+//! lengths.
+//!
+//! # Examples
+//!
+//! Compare two [`PrimitiveArray`]s:
+//! ```
+//! use arrow2::compute::comparison::{primitive_compare, Operator};
+//! # use arrow2::array::{BooleanArray, PrimitiveArray};
+//! # use arrow2::error::{ArrowError, Result};
+//!
+//! let array1 = PrimitiveArray::<i32>::from([Some(1), None, Some(2)]);
+//! let array2 = PrimitiveArray::<i32>::from([Some(1), None, Some(1)]);
+//! let result = primitive_compare(&array1, &array2, Operator::Gt)?;
+//! assert_eq!(result, BooleanArray::from([Some(false), None, Some(true)]));
+//! # Ok::<(), ArrowError>(())
+//! ```
+//! Compare two dynamically-typed arrays (trait objects):
+//! ```
+//! use arrow2::compute::comparison::{compare, Operator};
+//! # use arrow2::array::{Array, BooleanArray, PrimitiveArray};
+//! # use arrow2::error::{ArrowError, Result};
+//!
+//! let array1: &dyn Array = &PrimitiveArray::<f64>::from(&[Some(10.0), None, Some(20.0)]);
+//! let array2: &dyn Array = &PrimitiveArray::<f64>::from(&[Some(10.0), None, Some(10.0)]);
+//! let result = compare(array1, array2, Operator::LtEq)?;
+//! assert_eq!(result, BooleanArray::from([Some(true), None, Some(false)]));
+//! # Ok::<(), ArrowError>(())
+//! ```
+//! Compare an array of strings to a "scalar", i.e a word (note that we use
+//! [`Operator::Neq`]):
+//! ```
+//! use arrow2::compute::comparison::{utf8_compare_scalar, Operator};
+//! # use arrow2::array::{Array, BooleanArray, Utf8Array};
+//! # use arrow2::scalar::Utf8Scalar;
+//! # use arrow2::error::{ArrowError, Result};
+//!
+//! let array = Utf8Array::<i32>::from([Some("compute"), None, Some("compare")]);
+//! let word = Utf8Scalar::new(Some("compare"));
+//! let result = utf8_compare_scalar(&array, &word, Operator::Neq);
+//! assert_eq!(result, BooleanArray::from([Some(true), None, Some(false)]));
+//! # Ok::<(), ArrowError>(())
+//! ```
 
 use crate::array::*;
 use crate::datatypes::{DataType, IntervalUnit};
@@ -30,6 +90,17 @@ mod utf8;
 mod simd;
 pub use simd::{Simd8, Simd8Lanes};
 
+pub use binary::compare as binary_compare;
+pub use binary::compare_scalar as binary_compare_scalar;
+pub use boolean::compare as boolean_compare;
+pub use boolean::compare_scalar as boolean_compare_scalar;
+pub use primitive::compare as primitive_compare;
+pub use primitive::compare_scalar as primitive_compare_scalar;
+pub(crate) use primitive::compare_values_op as primitive_compare_values_op;
+pub use utf8::compare as utf8_compare;
+pub use utf8::compare_scalar as utf8_compare_scalar;
+
+/// Comparison operators, such as `>` ([`Operator::Gt`])
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum Operator {
     Lt,
@@ -262,13 +333,6 @@ pub fn compare_scalar(
         }
     })
 }
-
-pub use binary::compare_scalar_non_null as binary_compare_scalar;
-pub use boolean::compare_scalar_non_null as boolean_compare_scalar;
-pub use primitive::compare_scalar_non_null as primitive_compare_scalar;
-pub(crate) use primitive::compare_values_op as primitive_compare_values_op;
-pub use utf8::compare_scalar_non_null as utf8_compare_scalar;
-
 /// Checks if an array of type `datatype` can be compared with another array of
 /// the same type.
 ///

src/compute/comparison/primitive.rs

@@ -213,6 +213,13 @@ where
     compare_op_scalar(lhs, rhs, |a, b| a.gt_eq(b))
 }
 
+/// Compare two [`PrimitiveArray`]s using the given [`Operator`].
+///
+/// # Errors
+/// When the two arrays have different lengths.
+///
+/// Check the [crate::compute::comparison](module documentation) for usage
+/// examples.
 pub fn compare<T: NativeType + Simd8>(
     lhs: &PrimitiveArray<T>,
     rhs: &PrimitiveArray<T>,
@@ -228,6 +235,11 @@ pub fn compare<T: NativeType + Simd8>(
     }
 }
 
+/// Compare a [`PrimitiveArray`] and a scalar value using the given
+/// [`Operator`].
+///
+/// Check the [crate::compute::comparison](module documentation) for usage
+/// examples.
 pub fn compare_scalar<T: NativeType + Simd8>(
     lhs: &PrimitiveArray<T>,
     rhs: &PrimitiveScalar<T>,

src/compute/comparison/utf8.rs

@@ -121,6 +121,13 @@ fn gt_eq_scalar<O: Offset>(lhs: &Utf8Array<O>, rhs: &str) -> BooleanArray {
     compare_op_scalar(lhs, rhs, |a, b| a >= b)
 }
 
+/// Compare two [`Utf8Array`]s using the given [`Operator`].
+///
+/// # Errors
+/// When the two arrays have different lengths.
+///
+/// Check the [crate::compute::comparison](module documentation) for usage
+/// examples.
 pub fn compare<O: Offset>(
     lhs: &Utf8Array<O>,
     rhs: &Utf8Array<O>,
@@ -136,6 +143,11 @@ pub fn compare<O: Offset>(
     }
 }
 
+/// Compare a [`Utf8Array`] and a scalar value using the given
+/// [`Operator`].
+///
+/// Check the [crate::compute::comparison](module documentation) for usage
+/// examples.
 pub fn compare_scalar<O: Offset>(
     lhs: &Utf8Array<O>,
     rhs: &Utf8Scalar<O>,