test: add non x linear tests for xyReduce (#247)

src/xy/__tests__/xyReduce.test.ts

@@ -115,6 +115,29 @@ test('xyCheck optimization', () => {
   expect(result.y).toStrictEqual([0, 5, 10]);
 });
 
+test('xyCheck non-linear x', () => {
+  const xs = [];
+  const ys = [];
+  for (let i = 0; i < 11; i++) {
+    xs.push(i * 1.2 ** i);
+    ys.push(i);
+  }
+  const result = xyReduce({ x: xs, y: ys }, { nbPoints: 5 });
+  expect(result.y).toStrictEqual([0, 1, 8, 9, 10]);
+});
+
+test('xyCheck extreme non-linear x', () => {
+  const xs = [];
+  const ys = [];
+  for (let i = 0; i < 11; i++) {
+    xs.push(i * 2 ** i);
+    ys.push(i);
+  }
+  //console.log(xs, ys);
+  const result = xyReduce({ x: xs, y: ys }, { nbPoints: 5 });
+  expect(result.y).toStrictEqual([0, 1, 10]);
+});
+
 test('Part rounded far 2 with optimization', () => {
   const result = xyReduce({ x, y }, { nbPoints: 5, optimize: true });
 

src/xy/xyReduce.ts

@@ -29,7 +29,7 @@ export interface XYReduceOptions {
    * */
   nbPoints?: number;
   /**
-   * If optimize we may have less than nbPoints at the end
+   * If optimize we may have less than nbPoints at the end. It should not have visible effects
    * @default false
    * */
   optimize?: boolean;
@@ -42,7 +42,9 @@ export interface XYReduceOptions {
 
 /**
  * Reduce the number of points while keeping visually the same noise. Practical to
- * display many spectra as SVG. If you want a similar looking spectrum you should still however generate 4x the nbPoints that is being displayed.
+ * display many spectra as SVG. If you want a similar looking spectrum you should still however
+ * generate at least 4x the nbPoints that is being displayed.
+ *
  * SHOULD NOT BE USED FOR DATA PROCESSING !!!
  * You should rather use ml-xy-equally-spaced to make further processing
  *