alamb commented on code in PR #7882:
URL: https://github.com/apache/arrow-rs/pull/7882#discussion_r2198286609
##
arrow-ord/src/ord.rs:
##
@@ -915,4 +947,220 @@ mod tests {
assert_eq!(cmp(2, 0), Ordering::Equal); // (None, None) cmp (None,
None)
assert_eq!(cmp(3, 0), Ordering::Greater); // None cmp (None, None)
}
+
+#[test]
+fn test_map() {
+// Create first map array demonstrating key priority over values:
+// [{"a": 100, "b": 1}, {"b": 999, "c": 1}, {}, {"x": 1}]
+let string_builder = StringBuilder::new();
+let int_builder = Int32Builder::new();
+let mut map1_builder = MapBuilder::new(None, string_builder,
int_builder);
+
+// {"a": 100, "b": 1} - high value for "a", low value for "b"
+map1_builder.keys().append_value("a");
+map1_builder.values().append_value(100);
+map1_builder.keys().append_value("b");
+map1_builder.values().append_value(1);
+map1_builder.append(true).unwrap();
+
+// {"b": 999, "c": 1} - very high value for "b", low value for "c"
+map1_builder.keys().append_value("b");
+map1_builder.values().append_value(999);
+map1_builder.keys().append_value("c");
+map1_builder.values().append_value(1);
+map1_builder.append(true).unwrap();
+
+// {}
+map1_builder.append(true).unwrap();
+
+// {"x": 1}
+map1_builder.keys().append_value("x");
+map1_builder.values().append_value(1);
+map1_builder.append(true).unwrap();
+
+let map1 = map1_builder.finish();
+
+// Create second map array:
+// [{"a": 1, "c": 999}, {"b": 1, "d": 999}, {"a": 1}, None]
+let string_builder = StringBuilder::new();
+let int_builder = Int32Builder::new();
+let mut map2_builder = MapBuilder::new(None, string_builder,
int_builder);
+
+// {"a": 1, "c": 999} - low value for "a", high value for "c"
+map2_builder.keys().append_value("a");
+map2_builder.values().append_value(1);
+map2_builder.keys().append_value("c");
+map2_builder.values().append_value(999);
+map2_builder.append(true).unwrap();
+
+// {"b": 1, "d": 999} - low value for "b", high value for "d"
+map2_builder.keys().append_value("b");
+map2_builder.values().append_value(1);
+map2_builder.keys().append_value("d");
+map2_builder.values().append_value(999);
+map2_builder.append(true).unwrap();
+
+// {"a": 1}
+map2_builder.keys().append_value("a");
+map2_builder.values().append_value(1);
+map2_builder.append(true).unwrap();
+
+// None
+map2_builder.append(false).unwrap();
+
+let map2 = map2_builder.finish();
+
+let opts = SortOptions {
+descending: false,
+nulls_first: true,
+};
+let cmp = make_comparator(&map1, &map2, opts).unwrap();
+
+// Test that keys have priority over values:
+// {"a": 100, "b": 1} vs {"a": 1, "c": 999}
+// First entries match (a:100 vs a:1), but 100 > 1, so Greater
+assert_eq!(cmp(0, 0), Ordering::Greater);
+
+// {"b": 999, "c": 1} vs {"b": 1, "d": 999}
+// First entries match (b:999 vs b:1), but 999 > 1, so Greater
+assert_eq!(cmp(1, 1), Ordering::Greater);
+
+// Key comparison: "a" < "b", so {"a": 100, "b": 1} < {"b": 999, "c":
1}
+assert_eq!(cmp(0, 1), Ordering::Less);
+
+// Empty map vs non-empty
+assert_eq!(cmp(2, 2), Ordering::Less); // {} < {"a": 1}
+
+// Non-null vs null
+assert_eq!(cmp(3, 3), Ordering::Greater); // {"x": 1} > None
+
+// Key priority test: "x" > "a", regardless of values
+assert_eq!(cmp(3, 0), Ordering::Greater); // {"x": 1} > {"a": 1, "c":
999}
+
+// Empty vs non-empty
+assert_eq!(cmp(2, 0), Ordering::Less); // {} < {"a": 1, "c": 999}
+
+let opts = SortOptions {
+descending: true,
+nulls_first: true,
+};
+let cmp = make_comparator(&map1, &map2, opts).unwrap();
+
+// With descending=true, value comparison is reversed
+assert_eq!(cmp(0, 0), Ordering::Less); // {"a": 100, "b": 1} vs {"a":
1, "c": 999} (reversed)
+assert_eq!(cmp(1, 1), Ordering::Less); // {"b": 999, "c": 1} vs {"b":
1, "d": 999} (reversed)
+assert_eq!(cmp(0, 1), Ordering::Greater); // {"a": 100, "b": 1} vs
{"b": 999, "c": 1} (key order reversed)
+assert_eq!(cmp(3, 3), Ordering::Greater); // {"x": 1} > None
+assert_eq!(cmp(2, 2), Ordering::Greater); // {} > {"a": 1} (reversed)
+
+let opts = SortOptions {
+descending: false,
+nulls_first: false,
+};
+let cmp = make_comparator(&map1, &map2, opts).unwrap();
+
+// Same key priority behavior with nulls_first=false
+assert_eq!(cmp(0, 0), Ordering::Greater)
