[GitHub] [arrow] nevi-me commented on a change in pull request #8794: ARROW-10759: [Rust][DataFusion] Implement string to date cast

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

nevi-me commented on a change in pull request #8794:
URL: https://github.com/apache/arrow/pull/8794#discussion_r534625962



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File path: rust/arrow/src/compute/kernels/cast.rs
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@@ -376,6 +378,27 @@ pub fn cast(array: &ArrayRef, to_type: &DataType) -> Result<ArrayRef> {
             Int64 => cast_string_to_numeric::<Int64Type>(array),
             Float32 => cast_string_to_numeric::<Float32Type>(array),
             Float64 => cast_string_to_numeric::<Float64Type>(array),
+            Date32(DateUnit::Day) => {
+                use chrono::{NaiveDate, NaiveTime};
+                let zero_time = NaiveTime::from_hms(0, 0, 0);
+                let string_array = array.as_any().downcast_ref::<StringArray>().unwrap();
+                let mut builder = PrimitiveBuilder::<Date32Type>::new(string_array.len());
+                for i in 0..string_array.len() {
+                    if string_array.is_null(i) {
+                        builder.append_null()?;
+                    } else {
+                        match NaiveDate::parse_from_str(string_array.value(i), "%Y-%m-%d")
+                        {
+                            Ok(date) => builder.append_value(
+                                (date.and_time(zero_time).timestamp() / SECONDS_IN_DAY)
+                                    as i32,
+                            )?,
+                            Err(_) => builder.append_null()?, // not a valid date

Review comment:
       A possible solution is to add cast options (there's a JIRA open somewhere), which we can use to tweak the behaviour. We could look at the options in the C++ implementations.
   One cast option would be whether failed should return errors or be converted to nulls.




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