Implement cast method on Array and ChunkedArray (#79)

arro3-core/python/arro3/core/_core.pyi

@@ -49,6 +49,13 @@ class Array:
     def to_numpy(self) -> NDArray:
         """Return a numpy copy of this array."""
 
+    def cast(self, target_type: ArrowSchemaExportable) -> Array:
+        """Cast array values to another data type
+
+        Args:
+            target_type: Type to cast array to.
+        """
+
     def slice(self, offset: int = 0, length: int | None = None) -> Array:
         """Compute zero-copy slice of this array.
 
@@ -100,6 +107,12 @@ class ChunkedArray:
     @classmethod
     def from_arrow_pycapsule(cls, capsule) -> ChunkedArray:
         """Construct this object from a bare Arrow PyCapsule"""
+    def cast(self, target_type: ArrowSchemaExportable) -> ChunkedArray:
+        """Cast array values to another data type
+
+        Args:
+            target_type: Type to cast array to.
+        """
     def chunk(self, i: int) -> Array: ...
     @property
     def chunks(self) -> list[Array]: ...

pyo3-arrow/src/array.rs

@@ -257,6 +257,13 @@ impl PyArray {
         Ok(Self::from_array_ref(arrow_array))
     }
 
+    fn cast(&self, py: Python, target_type: PyDataType) -> PyArrowResult<PyObject> {
+        let target_type = target_type.into_inner();
+        let new_array = arrow::compute::cast(self.as_ref(), &target_type)?;
+        let new_field = self.field.as_ref().clone().with_data_type(target_type);
+        Ok(PyArray::new(new_array, new_field.into()).to_arro3(py)?)
+    }
+
     #[pyo3(signature = (offset=0, length=None))]
     pub fn slice(&self, py: Python, offset: usize, length: Option<usize>) -> PyResult<PyObject> {
         let length = length.unwrap_or_else(|| self.array.len() - offset);

pyo3-arrow/src/chunked.rs

@@ -309,6 +309,17 @@ impl PyChunkedArray {
         Ok(PyChunkedArray::new(chunks, field))
     }
 
+    fn cast(&self, py: Python, target_type: PyDataType) -> PyArrowResult<PyObject> {
+        let target_type = target_type.into_inner();
+        let new_chunks = self
+            .chunks
+            .iter()
+            .map(|chunk| arrow::compute::cast(&chunk, &target_type))
+            .collect::<Result<Vec<_>, ArrowError>>()?;
+        let new_field = self.field.as_ref().clone().with_data_type(target_type);
+        Ok(PyChunkedArray::new(new_chunks, new_field.into()).to_arro3(py)?)
+    }
+
     pub fn chunk(&self, py: Python, i: usize) -> PyResult<PyObject> {
         let field = self.field().clone();
         let array = self