[GitHub] [arrow-rs] sunchao commented on a diff in pull request #2608: Cast timestamp array to string array with timezone

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

sunchao commented on code in PR #2608:
URL: https://github.com/apache/arrow-rs/pull/2608#discussion_r959969219


##########
arrow/src/compute/kernels/temporal.rs:
##########
@@ -28,33 +28,33 @@ use chrono::format::{parse, Parsed};
 use chrono::FixedOffset;
 
 macro_rules! extract_component_from_array {
-    ($array:ident, $builder:ident, $extract_fn:ident, $using:ident) => {
+    ($array:ident, $builder:ident, $extract_fn:ident, $using:ident, $convert:expr) => {

Review Comment:
   why we need the `$convert`?



##########
arrow/src/compute/kernels/mod.rs:
##########
@@ -35,5 +35,6 @@ pub mod sort;
 pub mod substring;
 pub mod take;
 pub mod temporal;
+// pub(crate) use temporal::extract_component_from_array;

Review Comment:
   what is this for?



##########
arrow/src/compute/kernels/cast.rs:
##########
@@ -1482,25 +1487,35 @@ where
 }
 
 /// Cast timestamp types to Utf8/LargeUtf8
-fn cast_timestamp_to_string<T, OffsetSize>(array: &ArrayRef) -> Result<ArrayRef>
+fn cast_timestamp_to_string<T, OffsetSize>(
+    array: &ArrayRef,
+    tz: &Option<String>,
+) -> Result<ArrayRef>
 where
     T: ArrowTemporalType + ArrowNumericType,
     i64: From<<T as ArrowPrimitiveType>::Native>,
     OffsetSize: OffsetSizeTrait,
 {
     let array = array.as_any().downcast_ref::<PrimitiveArray<T>>().unwrap();
 
-    Ok(Arc::new(
-        (0..array.len())
-            .map(|ix| {
-                if array.is_null(ix) {
-                    None
-                } else {
-                    array.value_as_datetime(ix).map(|v| v.to_string())
-                }
-            })
-            .collect::<GenericStringArray<OffsetSize>>(),
-    ))
+    let mut builder = GenericStringBuilder::<OffsetSize>::new();
+
+    if let Some(tz) = tz {
+        let mut scratch = Parsed::new();
+        extract_component_from_array!(

Review Comment:
   it's not too obvious to see what this is doing, maybe add some comments?



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