Merge branch 'feature/41-add-median-function' into develop

Fixes #41

Author: delphidabbler

collection/665.dat

@@ -0,0 +1,18 @@
+function Median(A: array of Double): Double; overload;
+var
+  MiddleLo: Integer;
+begin
+  if System.Length(A) = 0 then
+    raise SysUtils.EArgumentException.Create('Array is empty');
+  // optimisations for array lengths 1 & 2 to avoid sorting
+  if System.Length(A) = 1 then
+    Exit(A[0]);
+  if System.Length(A) = 2 then
+    Exit((A[0] + A[1]) / 2.0);
+  Generics.Collections.TArray.Sort<Double>(A); // using standard comparer
+  MiddleLo := System.Length(A) div 2 - 1;
+  if System.Odd(System.Length(A)) then
+    Result := A[MiddleLo + 1]
+  else
+    Result := (A[MiddleLo] + A[MiddleLo + 1]) / 2.0;
+end;

collection/666.dat

@@ -0,0 +1,18 @@
+function Median(A: array of Integer): Double; overload;
+var
+  MiddleLo: Integer;
+begin
+  if System.Length(A) = 0 then
+    raise SysUtils.EArgumentException.Create('Array is empty');
+  // optimisations for array lengths 1 & 2 to avoid sorting
+  if System.Length(A) = 1 then
+    Exit(A[0]);
+  if System.Length(A) = 2 then
+    Exit((A[0] + A[1]) / 2);
+  Generics.Collections.TArray.Sort<Integer>(A); // using standard comparer
+  MiddleLo := System.Length(A) div 2 - 1;
+  if System.Odd(Length(A)) then
+    Result := A[MiddleLo + 1]
+  else
+    Result := (A[MiddleLo] + A[MiddleLo + 1]) / 2;
+end;

collection/maths.ini

@@ -1871,3 +1871,29 @@ AdvancedTest.URL="https://github.com/delphidabbler/code-snippets/tree/master/tes
 Snip=664.dat
 DelphiXE=Y
 Delphi12A=Y
+
+[Median_Double]
+DisplayName="Median (Double overload)"
+DescEx="<p>Returns the median of an array of floating point values.</p><p>Raises an <var>EArgumentException</var> exception if the array is empty.</p>"
+Kind=routine
+Units=SysUtils,Generics.Collections
+SeeAlso=Median_Integer
+TestInfo=advanced
+AdvancedTest.Level=unit-tests
+AdvancedTest.URL="https://github.com/delphidabbler/code-snippets/tree/master/tests/Cat-Maths"
+Snip=665.dat
+DelphiXE=Y
+Delphi12A=Y
+
+[Median_Integer]
+DisplayName="Median (Integer overload)"
+DescEx="<p>Returns the median of an array of integer values.</p><p>Raises an <var>EArgumentException</var> exception if the array is empty.</p>"
+Kind=routine
+Units=SysUtils,Generics.Collections
+SeeAlso=Median_Double
+TestInfo=advanced
+AdvancedTest.Level=unit-tests
+AdvancedTest.URL="https://github.com/delphidabbler/code-snippets/tree/master/tests/Cat-Maths"
+Snip=666.dat
+DelphiXE=Y
+Delphi12A=Y

tests/Cat-Maths/TestUMathsCatSnippets.pas

@@ -86,6 +86,8 @@   TestMathsCatSnippets = class(TTestCase)
     procedure TestIsNarcissistic;
     procedure TestLSE;    // required by SoftMax
     procedure TestSoftMax;
+    procedure TestMedian_Integer;
+    procedure TestMedian_Double;
   end;
 
 implementation
@@ -881,6 +883,38 @@ procedure TestMathsCatSnippets.TestMaxOfArray_Single;
   Check(SameValue(N, MaxOfArray(A)), 'Test 5');
 end;
 
+procedure TestMathsCatSnippets.TestMedian_Double;
+const
+  Fudge = 0.000001;
+  A1: array[1..1] of Double = (436.57);
+  A2: array[1..2] of Double = (-123.45, 170.05);
+  A5: array[1..5] of Double = (1.234, 4256.12345, 7000000000.0, PI, 0.000006758493);
+  A6: array[1..6] of Double = (4883.937382, 37473.0, 235.00001, -99.9282, 42.32654, 56.986382);
+  A7: array[1..7] of Double = (938298.0837, 729837.3627, 80001.34, 79876.46372, 67012.1234, 38983.12, 3500.93937);
+begin
+  CheckTrue(SameValue(436.57, Median(A1), Fudge), '#1');
+  CheckTrue(SameValue(23.3, Median(A2), Fudge), '#2');
+  CheckTrue(SameValue(PI, Median(A5), Fudge), '#5');
+  CheckTrue(SameValue(145.993196, Median(A6), Fudge), '#6');
+  CheckTrue(SameValue(79876.46372, Median(A7), Fudge), '#7');
+end;
+
+procedure TestMathsCatSnippets.TestMedian_Integer;
+const
+  A1: array[1..1] of Integer = (4);
+  A2: array[1..2] of Integer = (-6, 1);
+  A5: array[1..5] of Integer = (1, 3, 5, 7, 9);
+  A6: array[1..6] of Integer = (4883, 37473, 235, -99, 42, 56);
+  A7: array[1..7] of Integer = (77, 66, 55, 44, 33, 22, 11);
+begin
+  CheckTrue(SameValue(4.0, Median(A1)), '#1');
+  CheckTrue(SameValue(-2.5, Median(A2)), '#2');
+  CheckTrue(SameValue(5.0, Median(A5)), '#5');
+  CheckTrue(SameValue(145.5, Median(A6)), '#6');
+  CheckTrue(SameValue(44.0, Median(A7)), '#7');
+
+end;
+
 procedure TestMathsCatSnippets.TestMid_Double;
 var
   A, B, C, D, E: Double;

tests/Cat-Maths/UMathsCatSnippets.pas

@@ -6,7 +6,7 @@
  * The unit is copyright © 2005-2024 by Peter Johnson & Contributors and is
  * licensed under the MIT License (https://opensource.org/licenses/MIT).
  * 
- * Generated on : Fri, 10 Jan 2025 09:52:09 GMT.
+ * Generated on : Fri, 10 Jan 2025 19:22:03 GMT.
  * Generated by : DelphiDabbler CodeSnip Release 4.24.0.
  * 
  * The latest version of CodeSnip is available from the CodeSnip GitHub project
@@ -18,7 +18,7 @@
 interface
 
 uses
-  SysUtils, Math, Types, Windows;
+  SysUtils, Math, Types, Windows, Generics.Collections;
 
 {
   Encapsulates a point with double precision floating point coordinates.
@@ -268,6 +268,18 @@ function MaxOfArray(const A: array of Integer): Integer; overload;
 }
 function MaxOfArray(const A: array of Single): Single; overload;
 
+{
+  Returns the median of an array of floating point values.
+  Raises an EArgumentException exception if the array is empty.
+}
+function Median(A: array of Double): Double; overload;
+
+{
+  Returns the median of an array of integer values.
+  Raises an EArgumentException exception if the array is empty.
+}
+function Median(A: array of Integer): Double; overload;
+
 {
   Returns the middle of three double precision floating point values.
 }
@@ -1314,6 +1326,52 @@ function MaxOfArray(const A: array of Single): Single; overload;
       Result := A[Idx];
 end;
 
+{
+  Returns the median of an array of floating point values.
+  Raises an EArgumentException exception if the array is empty.
+}
+function Median(A: array of Double): Double; overload;
+var
+  MiddleLo: Integer;
+begin
+  if System.Length(A) = 0 then
+    raise SysUtils.EArgumentException.Create('Array is empty');
+  // optimisations for array lengths 1 & 2 to avoid sorting
+  if System.Length(A) = 1 then
+    Exit(A[0]);
+  if System.Length(A) = 2 then
+    Exit((A[0] + A[1]) / 2.0);
+  Generics.Collections.TArray.Sort<Double>(A); // using standard comparer
+  MiddleLo := System.Length(A) div 2 - 1;
+  if System.Odd(System.Length(A)) then
+    Result := A[MiddleLo + 1]
+  else
+    Result := (A[MiddleLo] + A[MiddleLo + 1]) / 2.0;
+end;
+
+{
+  Returns the median of an array of integer values.
+  Raises an EArgumentException exception if the array is empty.
+}
+function Median(A: array of Integer): Double; overload;
+var
+  MiddleLo: Integer;
+begin
+  if System.Length(A) = 0 then
+    raise SysUtils.EArgumentException.Create('Array is empty');
+  // optimisations for array lengths 1 & 2 to avoid sorting
+  if System.Length(A) = 1 then
+    Exit(A[0]);
+  if System.Length(A) = 2 then
+    Exit((A[0] + A[1]) / 2);
+  Generics.Collections.TArray.Sort<Integer>(A); // using standard comparer
+  MiddleLo := System.Length(A) div 2 - 1;
+  if System.Odd(Length(A)) then
+    Result := A[MiddleLo + 1]
+  else
+    Result := (A[MiddleLo] + A[MiddleLo + 1]) / 2;
+end;
+
 {
   Returns the middle of three double precision floating point values.
 }