[GitHub] [arrow-rs] askoa commented on a diff in pull request #3603: Add ArrayAccessor, Iterator, Extend and benchmarks for RunArray

["askoa (via GitHub)" <gi...@apache.org>]

askoa commented on code in PR #3603:
URL: https://github.com/apache/arrow-rs/pull/3603#discussion_r1092863125


##########
arrow-array/src/array/run_array.rs:
##########
@@ -274,15 +296,191 @@ pub type Int32RunArray = RunArray<Int32Type>;
 /// ```
 pub type Int64RunArray = RunArray<Int64Type>;
 
+/// A strongly-typed wrapper around a [`RunArray`] that implements [`ArrayAccessor`]
+/// and [`IntoIterator`] allowing fast access to its elements
+///
+/// ```
+/// use arrow_array::{RunArray, StringArray, types::Int32Type};
+///
+/// let orig = ["a", "b", "a", "b"];
+/// let ree_array = RunArray::<Int32Type>::from_iter(orig);
+///
+/// // `TypedRunArray` allows you to access the values directly
+/// let typed = ree_array.downcast_ref::<StringArray>().unwrap();
+///
+/// for (maybe_val, orig) in typed.into_iter().zip(orig) {
+///     assert_eq!(maybe_val.unwrap(), orig)
+/// }
+/// ```
+pub struct TypedRunArray<'a, R: RunEndIndexType, V> {
+    /// The run array
+    run_array: &'a RunArray<R>,
+
+    /// The values of the run_array
+    values: &'a V,
+}
+
+// Manually implement `Clone` to avoid `V: Clone` type constraint
+impl<'a, R: RunEndIndexType, V> Clone for TypedRunArray<'a, R, V> {
+    fn clone(&self) -> Self {
+        Self {
+            run_array: self.run_array,
+            values: self.values,
+        }
+    }
+}
+
+impl<'a, R: RunEndIndexType, V> Copy for TypedRunArray<'a, R, V> {}
+
+impl<'a, R: RunEndIndexType, V> std::fmt::Debug for TypedRunArray<'a, R, V> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        writeln!(f, "TypedRunArray({:?})", self.run_array)
+    }
+}
+
+impl<'a, R: RunEndIndexType, V> TypedRunArray<'a, R, V> {
+    /// Returns the run_ends of this [`TypedRunArray`]
+    pub fn run_ends(&self) -> &'a PrimitiveArray<R> {
+        self.run_array.run_ends()
+    }
+
+    /// Returns the values of this [`TypedRunArray`]
+    pub fn values(&self) -> &'a V {
+        self.values
+    }
+
+    /// Returns index to the physcial array for the given index to the logical array.
+    /// Performs a binary search on the run_ends array for the input index.
+    #[inline]
+    pub fn get_physical_index(&self, logical_index: usize) -> Option<usize> {
+        if logical_index >= self.run_array.len() {
+            return None;
+        }
+        let mut st: usize = 0;

Review Comment:
   To use `binary_search_by` a custom `Ordering` has to be implemented. Two values (`i` and `i-1`) has to be accessed to determine `std::cmp::Ordering::Equal`.  I am not sure what'll happen if `Equal` was never returned in custom `Ordering`. I did not spend lot of time on it because did not see the benefits.



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