Merge pull request #52 from observerly/feature/stats/performLinearReg…

…ression

src/stats/__tests__/regression.spec.ts

@@ -0,0 +1,118 @@
+/*****************************************************************************************************************/
+
+// @author         Michael Roberts <[email protected]>
+// @package        @observerly/fits
+// @license        Copyright © 2021-2025 observerly
+
+/*****************************************************************************************************************/
+
+import { describe, expect, it } from 'vitest'
+
+import { type Point, performLinearRegression } from '../regression'
+
+/*****************************************************************************************************************/
+
+describe('performLinearRegression', () => {
+  it('should correctly compute slope and intercept for a simple linear relationship', () => {
+    const points: Point[] = [
+      { x: 0, y: 1 },
+      { x: 1, y: 3 },
+      { x: 2, y: 5 },
+      { x: 3, y: 7 }
+    ]
+
+    const { m, c } = performLinearRegression(points)
+
+    expect(m).toBeCloseTo(2)
+    expect(c).toBeCloseTo(1)
+  })
+
+  it('should handle floating point values accurately', () => {
+    const points: Point[] = [
+      { x: 0.5, y: 2.1 },
+      { x: 1.5, y: 3.9 },
+      { x: 2.5, y: 5.8 },
+      { x: 3.5, y: 7.7 }
+    ]
+
+    const { m, c } = performLinearRegression(points)
+
+    expect(m).toBeCloseTo(1.867, 2)
+    expect(c).toBeCloseTo(1.135, 2)
+  })
+
+  it('should correctly compute slope and intercept for a vertical line-like data', () => {
+    const points: Point[] = [
+      { x: 1, y: 2 },
+      { x: 2, y: 4 },
+      { x: 3, y: 6 },
+      { x: 4, y: 8 }
+    ]
+
+    const { m, c } = performLinearRegression(points)
+    expect(m).toBeCloseTo(2)
+    expect(c).toBeCloseTo(0)
+  })
+
+  it('should handle negative slopes correctly', () => {
+    const points: Point[] = [
+      { x: 0, y: 10 },
+      { x: 1, y: 8 },
+      { x: 2, y: 6 },
+      { x: 3, y: 4 }
+    ]
+
+    const { m, c } = performLinearRegression(points)
+    expect(m).toBeCloseTo(-2)
+    expect(c).toBeCloseTo(10)
+  })
+
+  it('should handle points with zero variance in y', () => {
+    const points: Point[] = [
+      { x: 0, y: 5 },
+      { x: 1, y: 5 },
+      { x: 2, y: 5 },
+      { x: 3, y: 5 }
+    ]
+
+    const { m, c } = performLinearRegression(points)
+    expect(m).toBeCloseTo(0)
+    expect(c).toBeCloseTo(5)
+  })
+
+  it('should compute correct values for a random set of points', () => {
+    const points: Point[] = [
+      { x: 1, y: 2 },
+      { x: 2, y: 3 },
+      { x: 3, y: 5 },
+      { x: 4, y: 4 },
+      { x: 5, y: 6 }
+    ]
+
+    const { m, c } = performLinearRegression(points)
+    expect(m).toBeCloseTo(0.9)
+    expect(c).toBeCloseTo(1.3)
+  })
+
+  it('should throw an error when no points are provided', () => {
+    const points: Point[] = []
+
+    expect(() => performLinearRegression(points)).toThrow(
+      'No valid points provided for linear regression.'
+    )
+  })
+
+  it('should throw an error when all x values are the same', () => {
+    const points: Point[] = [
+      { x: 2, y: 3 },
+      { x: 2, y: 4 },
+      { x: 2, y: 5 }
+    ]
+
+    expect(() => performLinearRegression(points)).toThrow(
+      'Denominator is zero. Cannot compute linear regression.'
+    )
+  })
+})
+
+/*****************************************************************************************************************/

src/stats/index.ts

@@ -8,6 +8,7 @@
 
 export { mean } from './mean'
 export { median } from './median'
+export { performLinearRegression, type Point } from './regression'
 export { variance } from './variance'
 
 /*****************************************************************************************************************/

src/stats/regression.ts

@@ -0,0 +1,61 @@
+/*****************************************************************************************************************/
+
+// @author         Michael Roberts <michael@observerly>
+// @package        @observerly/fits
+// @license        Copyright © 2021-2025 observerly
+
+/*****************************************************************************************************************/
+
+export type Point = {
+  x: number
+  y: number
+}
+
+/*****************************************************************************************************************/
+
+/**
+ *
+ * performLinearRegression
+ *
+ * Calculates the linear regression (slope and intercept) for a set of points.
+ * This is crucial for identifying the trend within the pixel data, enabling effective contrast adjustment.
+ *
+ * @param points: Array of points containing x and y coordinates.
+ * @returns: An object containing the y-intercept (`c`) and the slope (`m`) of the fitted line.
+ * @throws Will throw an error if there is insufficient variation in the x-values.
+ */
+export function performLinearRegression(points: Point[]): { m: number; c: number } {
+  const n = points.length
+
+  if (n === 0) {
+    throw new Error('No valid points provided for linear regression.')
+  }
+
+  // Aggregate sums required for calculating slope and intercept using reduce for immutability and clarity:
+  const { sumX, sumY, sumXY, sumX2 } = points.reduce(
+    (acc, { x, y }) => ({
+      sumX: acc.sumX + x,
+      sumY: acc.sumY + y,
+      sumXY: acc.sumXY + x * y,
+      sumX2: acc.sumX2 + x ** 2
+    }),
+    { sumX: 0, sumY: 0, sumXY: 0, sumX2: 0 }
+  )
+
+  // Calculate the denominator to ensure there is enough variation in x-values for a valid regression:
+  const denominator = n * sumX2 - sumX ** 2
+
+  if (denominator === 0) {
+    throw new Error('Denominator is zero. Cannot compute linear regression.')
+  }
+
+  // Compute the slope (m) of the best-fit line:
+  const m = (n * sumXY - sumX * sumY) / denominator
+
+  // Compute the y-intercept (c) of the best-fit line:
+  const c = (sumY - m * sumX) / n
+
+  return { m, c }
+}
+
+/*****************************************************************************************************************/