add mean

src/min-max-range.ts

@@ -29,6 +29,7 @@ import {
   isNumber,
   map,
   max as maxOfArray,
+  mean as meanOfArray,
   min as minOfArray,
   pipe,
   ret,
@@ -42,7 +43,7 @@ import {
 export function bottomLeft(range: Range2D): Coordinates {
   return pipe(
     asRange2D,
-    (range: Range2D) => [min(range[0]), min(range[1])],
+    (range: Range2D) => [asNumber(min(range[0])), asNumber(min(range[1]))],
   )(range);
 }
 
@@ -54,7 +55,7 @@ export function bottomLeft(range: Range2D): Coordinates {
 export function bottomRight(range: Range2D): Coordinates {
   return pipe(
     asRange2D,
-    (range: Range2D) => [max(range[0]), min(range[1])],
+    (range: Range2D) => [asNumber(max(range[0])), asNumber(min(range[1]))],
   )(range);
 }
 
@@ -69,7 +70,7 @@ export function first(range: Range): undefined | number | number[] {
     alternative(
       pipe(
         asRange1D,
-        (range: Range1D) => range[0],
+        (range: Range1D) => asNumber(range[0]),
       ),
       pipe(
         asMultiDimRange,
@@ -139,7 +140,7 @@ export function last(range: Range): undefined | number | number[] {
     alternative(
       pipe(
         asRange1D,
-        (range: Range1D) => range[1],
+        (range: Range1D) => asNumber(range[1]),
       ),
       pipe(
         asMultiDimRange,
@@ -194,6 +195,28 @@ export function max(range: Range): undefined | number | number[] {
   )(range);
 }
 
+/**
+ * Return mean of each dimension of a range.
+ * @param   range The range.
+ * @returns       Mean of each dimension of the range.
+ */
+export function mean(range: Range): undefined | number | number[] {
+  return pipe(
+    asRange,
+    alternative(
+      pipe(
+        asRange1D,
+        meanOfArray,
+      ),
+      pipe(
+        asMultiDimRange,
+        map((el: Range1D) => asNumber(mean(el))),
+      ),
+      ret(undefined),
+    ),
+  )(range);
+}
+
 /**
  * Return minimum value of each dimension of a range.
  * @param   range The range.
@@ -227,7 +250,7 @@ export function reverse(range: Range): Range {
     alternative(
       pipe(
         asRange1D,
-        (range: Range1D) => [last(range), first(range)],
+        (range: Range1D) => [asNumber(last(range)), asNumber(first(range))],
       ),
       pipe(
         asMultiDimRange,
@@ -250,7 +273,7 @@ export function sort(range: Range): Range {
     alternative(
       pipe(
         asRange1D,
-        (range: Range1D) => [min(range), max(range)],
+        (range: Range1D) => [asNumber(min(range)), asNumber(max(range))],
       ),
       pipe(
         asMultiDimRange,

src/utils.ts

@@ -187,6 +187,15 @@ export function max(values: number[]): number {
   return Math.max(...values);
 }
 
+/**
+ * Return mean of values.
+ * @param   values Array of numbers.
+ * @returns        Mean value.
+ */
+export function mean(values: number[]): number {
+  return sum(values) / values.length;
+}
+
 /**
  * Return minimum value of array of numbers.
  * @param   values Array of numbers.
@@ -214,3 +223,12 @@ export function pipe(...transforms: Transform[]): Transform {
 export function ret<T>(value: T): () => T {
   return () => value;
 }
+
+/**
+ * Return sum of values.
+ * @param   values Array of numbers
+ * @returns        The sum.
+ */
+export function sum(values: number[]): number {
+  return values.reduce((sum, value) => sum + value, 0);
+}

test/min-max-range.test.ts

@@ -10,6 +10,7 @@ import {
   last,
   length,
   max,
+  mean,
   min,
   reverse,
   sort,
@@ -258,6 +259,31 @@ describe('min-max-range', () => {
     });
   });
 
+  describe('mean', () => {
+    it('throws an error if input is no range', () => {
+      for (const INVALID_RANGE of INVALID_RANGES) {
+        expect(() => {
+          mean(INVALID_RANGE);
+        }).toThrowError();
+      }
+    });
+
+    it('returns undefined for empty range', () => {
+      expect(mean(EMPTY_RANGE)).toBe(undefined);
+    });
+
+    it('returns arithmetic mean of one-dimensional range', () => {
+      expect(mean(RANGE_1D)).toBe((RANGE_1D[0] + RANGE_1D[1]) / 2);
+    });
+
+    it('returns arithmetic mean of multi-dimensional range', () => {
+      for (const MULTI_DIM_RANGE of MULTI_DIM_RANGES) {
+        expect(mean(MULTI_DIM_RANGE))
+          .toEqual(MULTI_DIM_RANGE.map(r => (r[0] + r[1]) / 2));
+      }
+    });
+  });
+
   describe('min', () => {
     it('throws an error if input is no range', () => {
       for (const INVALID_RANGE of INVALID_RANGES) {

test/utils.test.ts

@@ -12,9 +12,11 @@ import {
   isNumber,
   map,
   max,
+  mean,
   min,
   pipe,
   ret,
+  sum,
   Transform,
 } from '../src/utils';
 
@@ -261,8 +263,14 @@ describe('utils', () => {
     });
   });
 
+  describe('mean', () => {
+    it('returns the arithmetic mean of an array of numbers', () => {
+      expect(mean([4, 0, -6, 3])).toBe(0.25);
+    });
+  });
+
   describe('min', () => {
-    it('returns the minimum value of an array of number', () => {
+    it('returns the minimum value of an array of numbers', () => {
       expect(min([-3, 5, 0, -12])).toBe(-12);
     });
   });
@@ -287,4 +295,10 @@ describe('utils', () => {
       expect(returner()).toBe(42);
     });
   });
+
+  describe('sum', () => {
+    it('returns the sum of an array of numbers', () => {
+      expect(sum([-2, 4, -8, 16, -32, 64])).toBe(42);
+    });
+  });
 });