[GitHub] [arrow-rs] wjones127 commented on a diff in pull request #3925: feat: add take for MapArray

["wjones127 (via GitHub)" <gi...@apache.org>]

wjones127 commented on code in PR #3925:
URL: https://github.com/apache/arrow-rs/pull/3925#discussion_r1147061867


##########
arrow-array/src/array/map_array.rs:
##########
@@ -251,6 +251,69 @@ impl std::fmt::Debug for MapArray {
     }
 }
 
+impl TryFrom<&ListArray> for MapArray {
+    type Error = ArrowError;
+    fn try_from(value: &ListArray) -> Result<Self, Self::Error> {
+        let field = match value.data_type() {
+            DataType::List(field) => {
+                if let DataType::Struct(fields) = field.data_type() {
+                    if fields.len() != 2 {
+                        Err(ArrowError::InvalidArgumentError(
+                            "List item must be a struct type with two fields".to_string(),
+                        ))
+                    } else {
+                        Ok(field)
+                    }
+                } else {
+                    Err(ArrowError::InvalidArgumentError(
+                        "List item must be a struct type to convert to a list"
+                            .to_string(),
+                    ))
+                }
+            }
+            _ => unreachable!("This should be a list type."),
+        }?;
+        let old_data = value.to_data();
+        let array_data = unsafe {
+            ArrayData::new_unchecked(
+                DataType::Map(field.clone(), false),
+                old_data.len(),
+                Some(old_data.null_count()),
+                old_data.nulls().map(|nulls|nulls.buffer().clone()),
+                old_data.offset(),
+                old_data.buffers().to_vec(),
+                old_data.child_data().to_vec(),
+            )
+        };

Review Comment:
   Is there a better way to create a copy of `ArrayData` that's the same except for the type?



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