feat: add @math.(max|min)imum_by_key

math/algebraic.mbt

@@ -30,6 +30,25 @@ pub fn maximum[T : Compare](x : T, y : T) -> T {
   }
 }
 
+/// Returns the element that gives the maximum value from the specified function.
+///
+/// Returns the second argument if the comparison determines them to be equal.
+///
+/// # Examples
+///
+/// ```
+/// let abs = fn(n : Int) { if n < 0 { 0 - n } else { n } }
+/// print(@math.maximum_by_key(-2, 1, abs)) // output: -2
+/// print(@math.maximum_by_key(-2, 2, abs)) // output: 2
+/// ```
+pub fn maximum_by_key[T, K : Compare](x : T, y : T, f : (T) -> K) -> T {
+  if f(x) > f(y) {
+    x
+  } else {
+    y
+  }
+}
+
 /// Compares and returns the minimum of two values.
 ///
 /// Returns the first argument if the comparison determines them to be equal.
@@ -47,3 +66,22 @@ pub fn minimum[T : Compare](x : T, y : T) -> T {
     x
   }
 }
+
+/// Returns the element that gives the minimum value from the specified function.
+///
+/// Returns the first argument if the comparison determines them to be equal.
+///
+/// # Examples
+///
+/// ```
+/// let abs = fn(n : Int) { if n < 0 { 0 - n } else { n } }
+/// print(@math.minimum_by_key(-2, 1, abs)) // output: 1
+/// print(@math.minimum_by_key(-2, 2, abs)) // output: -2
+/// ```
+pub fn minimum_by_key[T, K : Compare](x : T, y : T, f : (T) -> K) -> T {
+  if f(x) > f(y) {
+    y
+  } else {
+    x
+  }
+}

math/algebraic_test.mbt

@@ -33,6 +33,13 @@ test "maximum.ref" {
   @test.is!(@math.maximum(x2t, x2), x2)
 }
 
+test "maximum_by_key" {
+  let abs = fn(n : Int) { if n < 0 { 0 - n } else { n } }
+  assert_eq!(@math.maximum_by_key(1, -2, abs), -2)
+  assert_eq!(@math.maximum_by_key(-2, 1, abs), -2)
+  assert_eq!(@math.maximum_by_key(-2, 2, abs), 2)
+}
+
 test "minimum.value" {
   assert_eq!(@math.minimum(1, 2), 1)
   assert_eq!(@math.minimum(2, 1), 1)
@@ -54,6 +61,13 @@ test "minimum.ref" {
   @test.is!(@math.minimum(x2t, x2), x2t)
 }
 
+test "minimum_by_key" {
+  let abs = fn(n : Int) { if n < 0 { 0 - n } else { n } }
+  assert_eq!(@math.minimum_by_key(1, -2, abs), 1)
+  assert_eq!(@math.minimum_by_key(-2, 1, abs), 1)
+  assert_eq!(@math.minimum_by_key(-2, 2, abs), -2)
+}
+
 test "exp" {
   assert_eq!(@math.exp(1), 2.718281828459045)
   assert_eq!(@math.exp(-1), 0.36787944117144233)

math/math.mbti

@@ -25,8 +25,12 @@ fn log2(Double) -> Double
 
 fn maximum[T : Compare + Eq](T, T) -> T
 
+fn maximum_by_key[T, K : Compare + Eq](T, T, (T) -> K) -> T
+
 fn minimum[T : Compare + Eq](T, T) -> T
 
+fn minimum_by_key[T, K : Compare + Eq](T, T, (T) -> K) -> T
+
 let pi : Double
 
 fn round(Double) -> Double