Only get displayer for the interesting field

src/array/display.rs

@@ -209,14 +209,9 @@ pub fn get_value_display<'a>(array: &'a dyn Array) -> Box<dyn Fn(usize) -> Strin
         }
         Union(_, _, _) => {
             let array = array.as_any().downcast_ref::<UnionArray>().unwrap();
-            let displays = array
-                .fields()
-                .iter()
-                .map(|x| get_display(x.as_ref()))
-                .collect::<Vec<_>>();
             Box::new(move |row: usize| {
                 let (field, index) = array.index(row);
-                displays[field](index)
+                get_display(array.fields()[field].as_ref())(index)
             })
         }
         Extension(_, _, _) => todo!(),