tinfoil-knight commented on code in PR #10117:
URL: https://github.com/apache/datafusion/pull/10117#discussion_r1590813568
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datafusion/expr/src/signature.rs:
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@@ -346,13 +346,81 @@ impl Signature {
}
}
-/// Monotonicity of the `ScalarFunctionExpr` with respect to its arguments.
-/// Each element of this vector corresponds to an argument and indicates
whether
-/// the function's behavior is monotonic, or non-monotonic/unknown for that
argument, namely:
-/// - `None` signifies unknown monotonicity or non-monotonicity.
-/// - `Some(true)` indicates that the function is monotonically increasing
w.r.t. the argument in question.
-/// - Some(false) indicates that the function is monotonically decreasing
w.r.t. the argument in question.
-pub type FuncMonotonicity = Vec<Option<bool>>;
+#[derive(Debug, Clone)]
+enum FuncMonotonicityPartial {
+ /// not monotonic or unknown monotonicity
+ None,
+ /// Increasing with respect to all of its arguments
+ Increasing,
+ /// Decreasing with respect to all of its arguments
+ Decreasing,
+ /// Each element of this vector corresponds to an argument and indicates
whether
+ /// the function's behavior is monotonic, or non-monotonic/unknown for
that argument, namely:
+ /// - `None` signifies unknown monotonicity or non-monotonicity.
+ /// - `Some(true)` indicates that the function is monotonically increasing
w.r.t. the argument in question.
+ /// - Some(false) indicates that the function is monotonically decreasing
w.r.t. the argument in question.
+ Mixed(Vec<Option<bool>>),
+}
+
+/// Monotonicity of a function with respect to its arguments.
+///
+/// A function is [monotonic] if it preserves the relative order of its inputs.
+///
+/// [monotonic]: https://en.wikipedia.org/wiki/Monotonic_function
+#[derive(Debug, Clone)]
+pub struct FuncMonotonicity(FuncMonotonicityPartial);
+
+impl FuncMonotonicity {
+ pub fn new_none() -> Self {
+ Self(FuncMonotonicityPartial::None)
+ }
+ pub fn new_increasing() -> Self {
+ Self(FuncMonotonicityPartial::Increasing)
+ }
+ pub fn new_decreasing() -> Self {
+ Self(FuncMonotonicityPartial::Decreasing)
+ }
+ pub fn new_mixed(inner: Vec<Option<bool>>) -> Self {
+ Self(FuncMonotonicityPartial::Mixed(inner))
+ }
+
+ /// returns true if this function is monotonically increasing with respect
to argument number arg
+ pub fn arg_increasing(&self, arg: usize) -> bool {
+ match &self.0 {
+ FuncMonotonicityPartial::None => false,
+ FuncMonotonicityPartial::Increasing => true,
+ FuncMonotonicityPartial::Decreasing => false,
+ FuncMonotonicityPartial::Mixed(inner) =>
inner[arg].unwrap_or(false),
+ }
+ }
+
+ /// returns true if this function is monotonically decreasing with respect
to argument number arg
+ pub fn arg_decreasing(&self, arg: usize) -> bool {
+ match &self.0 {
+ FuncMonotonicityPartial::None => false,
+ FuncMonotonicityPartial::Increasing => false,
+ FuncMonotonicityPartial::Decreasing => true,
+ FuncMonotonicityPartial::Mixed(inner) =>
inner[arg].unwrap_or(false),
+ }
Review Comment:
These APIs aren't being used anywhere. I think we can just remove them.
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