[GitHub] [arrow-rs] tustvold commented on a diff in pull request #1912: Add `DictionaryArray::key` function

[GitBox <gi...@apache.org>]

tustvold commented on code in PR #1912:
URL: https://github.com/apache/arrow-rs/pull/1912#discussion_r901284237


##########
arrow/src/array/array_dictionary.rs:
##########
@@ -169,6 +169,17 @@ impl<'a, K: ArrowPrimitiveType> DictionaryArray<K> {
             .iter()
             .map(|key| key.map(|k| k.to_usize().expect("Dictionary index not usize")))
     }
+
+    /// Return the value of `keys` (the dictionary key) at index `i`,
+    /// cast to `usize`, `None` if the value at `i` is `NULL`.
+    pub fn key(&self, i: usize) -> Option<usize> {
+        self.keys.is_valid(i).then(|| {
+            self.keys
+                .value(i)
+                .to_usize()
+                .expect("Dictionary index not usize")

Review Comment:
   Panicking should be fine, it's a validation failure if the array contains negative indexes. TBH I keep meaning to change all these checked conversions to numeric casts (i.e. as), I wouldn't be surprised if this leads to non-trivial performance benefits.



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