perf: avoid extra array copies in xy median and scan helpers

src/x/xMedian.ts

@@ -8,6 +8,18 @@ interface XMedianOptions {
    * @default false
    */
   exact?: boolean;
+
+  /**
+   * First index (inclusive) of the range to consider.
+   * @default 0
+   */
+  fromIndex?: number;
+
+  /**
+   * Last index (exclusive) of the range to consider.
+   * @default input.length
+   */
+  toIndex?: number;
 }
 
 /**
@@ -24,13 +36,17 @@ export function xMedian(
     throw new TypeError('input must be an array');
   }
 
-  if (input.length === 0) {
+  const {
+    exact = false,
+    fromIndex = 0,
+    toIndex = input.length,
+  } = options || {};
+  const array = input.slice(fromIndex, toIndex);
+
+  if (array.length === 0) {
     throw new TypeError('input must not be empty');
   }
 
-  const { exact = false } = options || {};
-  const array = input.slice();
-
   const middleIndex = calcMiddle(0, array.length - 1);
 
   const median = quickSelect(array, middleIndex);

src/xy/xyAlign.ts

@@ -99,10 +99,6 @@ export function xyAlign(
         i++;
       }
     } else {
-      const weightedX =
-        (data1.x[i] * data1.y[i] + data2.x[j] * data2.y[j]) /
-        (data1.y[i] + data2.y[j]);
-
       switch (x) {
         case 'x1':
           result.x.push(data1.x[i]);
@@ -111,7 +107,10 @@ export function xyAlign(
           result.x.push(data2.x[j]);
           break;
         case 'weighted':
-          result.x.push(weightedX);
+          result.x.push(
+            (data1.x[i] * data1.y[i] + data2.x[j] * data2.y[j]) /
+              (data1.y[i] + data2.y[j]),
+          );
           break;
         default:
           throw new Error(`unknown x option value: ${String(x)}`);

src/xy/xyMaxY.ts

@@ -42,7 +42,7 @@ export function xyMaxY(data: DataXY, options: XYMaxYOptions = {}): number {
   const { fromIndex, toIndex } = xGetFromToIndex(x, options);
 
   let currentxyMaxY = y[fromIndex];
-  for (let i = fromIndex; i <= toIndex; i++) {
+  for (let i = fromIndex + 1; i <= toIndex; i++) {
     if (y[i] > currentxyMaxY) currentxyMaxY = y[i];
   }
 

src/xy/xyMaxYPoint.ts

@@ -48,7 +48,7 @@ export function xyMaxYPoint(
   const { fromIndex, toIndex } = xGetFromToIndex(x, options);
 
   let current = { x: x[fromIndex], y: y[fromIndex], index: fromIndex };
-  for (let i = fromIndex; i <= toIndex; i++) {
+  for (let i = fromIndex + 1; i <= toIndex; i++) {
     if (y[i] > current.y) current = { x: x[i], y: y[i], index: i };
   }
 

src/xy/xyMedian.ts

@@ -31,6 +31,7 @@ export function xyMedian(data: DataXY): number {
     if (cumSumY > sumY / 2) {
       return x[i];
     } else if (cumSumY === sumY / 2) {
+      if (i === x.length - 1) return x[i];
       return 0.5 * (x[i] + x[i + 1]);
     }
   }

src/xy/xyMedianY.ts

@@ -26,10 +26,7 @@ export function xyMedianY(
   for (let i = 0; i < y.length; i++) {
     const fromIndex = Math.max(0, i - halfWindow);
     const toIndex = Math.min(y.length, i + halfWindow + 1);
-    const window = ArrayBuffer.isView(y)
-      ? y.subarray(fromIndex, toIndex)
-      : y.slice(fromIndex, toIndex);
-    result[i] = xMedian(window, { exact: false });
+    result[i] = xMedian(y, { exact: false, fromIndex, toIndex });
   }
 
   return { x, y: result };

src/xy/xyMedianYAtXs.ts

@@ -32,10 +32,7 @@ export function xyMedianYAtXs(
     const centerIndex = xFindClosestIndex(x, xValues[i]);
     const fromIndex = Math.max(0, centerIndex - halfWindow);
     const toIndex = Math.min(y.length, centerIndex + halfWindow + 1);
-    const window = ArrayBuffer.isView(y)
-      ? y.subarray(fromIndex, toIndex)
-      : y.slice(fromIndex, toIndex);
-    result[i] = xMedian(window, { exact: false });
+    result[i] = xMedian(y, { exact: false, fromIndex, toIndex });
   }
 
   return { x: xValues, y: result };

src/xy/xyMinYPoint.ts

@@ -49,7 +49,7 @@ export function xyMinYPoint(
     y: y[fromIndex],
     index: fromIndex,
   };
-  for (let i = fromIndex; i <= toIndex; i++) {
+  for (let i = fromIndex + 1; i <= toIndex; i++) {
     if (y[i] < current.y) current = { x: x[i], y: y[i], index: i };
   }