diff --git a/.gitignore b/.gitignore
index 7dea02f3..bf34965b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -44,3 +44,4 @@ dist
 
 .DS_Store
 .eslintcache
+.claude
diff --git a/src/__tests__/__snapshots__/index.test.ts.snap b/src/__tests__/__snapshots__/index.test.ts.snap
index 0107959e..f87c96fe 100644
--- a/src/__tests__/__snapshots__/index.test.ts.snap
+++ b/src/__tests__/__snapshots__/index.test.ts.snap
@@ -91,6 +91,7 @@ exports[`existence of exported functions 1`] = `
   "xyEquallySpaced",
   "xyExtract",
   "xyFilter",
+  "xyFromInterleaved",
   "xyFilterMinYValue",
   "xyFilterTopYValues",
   "xyFilterX",
@@ -124,6 +125,7 @@ exports[`existence of exported functions 1`] = `
   "xyRollingCircleTransform",
   "xySetYValue",
   "xySortX",
+  "xyToInterleaved",
   "xyToXYArray",
   "xyToXYObject",
   "xyUniqueX",
diff --git a/src/matrix/matrixPQN.ts b/src/matrix/matrixPQN.ts
index f72cfa20..c1094ab3 100644
--- a/src/matrix/matrixPQN.ts
+++ b/src/matrix/matrixPQN.ts
@@ -32,7 +32,7 @@ export function matrixPQN(
   medianOfQuotients: number[];
 } {
   const { max = 100 } = options;
-  const matrixB = new Matrix(matrix as number[][]);
+  const matrixB = new Matrix(matrix);
   for (let i = 0; i < matrixB.rows; i++) {
     const normalizationFactor = matrixB.getRowVector(i).norm('frobenius') / max;
     const row = matrixB.getRowVector(i).div(normalizationFactor);
diff --git a/src/utils/__tests__/calculateAdaptiveWeights.test.ts b/src/utils/__tests__/calculateAdaptiveWeights.test.ts
index 14c8fe2f..ca68c153 100644
--- a/src/utils/__tests__/calculateAdaptiveWeights.test.ts
+++ b/src/utils/__tests__/calculateAdaptiveWeights.test.ts
@@ -134,12 +134,7 @@ test('works with different array types', () => {
   const baseline = [1.1, 2.1, 3.1, 4.1, 5.1];
   const weights = [1, 1, 1, 1, 1];
 
-  const result = calculateAdaptiveWeights(
-    yData as any,
-    baseline as any,
-    weights as any,
-    {},
-  );
+  const result = calculateAdaptiveWeights(yData, baseline, weights, {});
 
   expect(result).toBeDefined();
   expect(result[0]).toBe(1);
diff --git a/src/xy/__tests__/xyFromInterleaved.test.ts b/src/xy/__tests__/xyFromInterleaved.test.ts
new file mode 100644
index 00000000..2ed0f5dc
--- /dev/null
+++ b/src/xy/__tests__/xyFromInterleaved.test.ts
@@ -0,0 +1,30 @@
+import { expect, test } from 'vitest';
+
+import { xyFromInterleaved } from '../index.ts';
+
+test('basic', () => {
+  expect(xyFromInterleaved([1, 10, 2, 20, 3, 30])).toStrictEqual({
+    x: new Float64Array([1, 2, 3]),
+    y: new Float64Array([10, 20, 30]),
+  });
+});
+
+test('Float64Array input', () => {
+  expect(xyFromInterleaved(new Float64Array([1, 10, 2, 20]))).toStrictEqual({
+    x: new Float64Array([1, 2]),
+    y: new Float64Array([10, 20]),
+  });
+});
+
+test('empty array', () => {
+  expect(xyFromInterleaved([])).toStrictEqual({
+    x: new Float64Array(0),
+    y: new Float64Array(0),
+  });
+});
+
+test('odd length throws', () => {
+  expect(() => xyFromInterleaved([1, 2, 3])).toThrow(
+    /data length must be even/,
+  );
+});
diff --git a/src/xy/__tests__/xyToInterleaved.test.ts b/src/xy/__tests__/xyToInterleaved.test.ts
new file mode 100644
index 00000000..37147502
--- /dev/null
+++ b/src/xy/__tests__/xyToInterleaved.test.ts
@@ -0,0 +1,21 @@
+import { expect, test } from 'vitest';
+
+import { xyFromInterleaved, xyToInterleaved } from '../index.ts';
+
+test('basic', () => {
+  expect(xyToInterleaved({ x: [1, 2, 3], y: [10, 20, 30] })).toStrictEqual(
+    new Float64Array([1, 10, 2, 20, 3, 30]),
+  );
+});
+
+test('empty', () => {
+  expect(xyToInterleaved({ x: [], y: [] })).toStrictEqual(new Float64Array(0));
+});
+
+test('round-trip with xyFromInterleaved', () => {
+  const interleaved = new Float64Array([1, 10, 2, 20, 3, 30]);
+
+  expect(xyToInterleaved(xyFromInterleaved(interleaved))).toStrictEqual(
+    interleaved,
+  );
+});
diff --git a/src/xy/index.ts b/src/xy/index.ts
index a8a9b914..472429d3 100644
--- a/src/xy/index.ts
+++ b/src/xy/index.ts
@@ -7,6 +7,7 @@ export * from './xyEnsureGrowingX.ts';
 export * from './xyEquallySpaced.ts';
 export * from './xyExtract.ts';
 export * from './xyFilter.ts';
+export * from './xyFromInterleaved.ts';
 export * from './xyFilterMinYValue.ts';
 export * from './xyFilterTopYValues.ts';
 export * from './xyFilterX.ts';
@@ -41,6 +42,7 @@ export * from './xyRolling.ts';
 export * from './xyRollingCircleTransform.ts';
 export * from './xySetYValue.ts';
 export * from './xySortX.ts';
+export * from './xyToInterleaved.ts';
 export * from './xyToXYArray.ts';
 export * from './xyToXYObject.ts';
 export * from './xyUniqueX.ts';
diff --git a/src/xy/xyFilterX.ts b/src/xy/xyFilterX.ts
index aad0d0a9..1fecd9ec 100644
--- a/src/xy/xyFilterX.ts
+++ b/src/xy/xyFilterX.ts
@@ -47,11 +47,12 @@ export function xyFilterX(
   }
   const {
     from = x[0],
-    to = x.at(-1) as number,
+    to = x.at(-1),
     zones = [{ from, to }],
     exclusions = [],
   } = options;
 
+  // @ts-expect-error -- x.at(-1) returns number | undefined but array is guaranteed non-empty here
   const normalizedZones = zonesNormalize(zones, { from, to, exclusions });
 
   let currentZoneIndex = 0;
diff --git a/src/xy/xyFromInterleaved.ts b/src/xy/xyFromInterleaved.ts
new file mode 100644
index 00000000..63d11068
--- /dev/null
+++ b/src/xy/xyFromInterleaved.ts
@@ -0,0 +1,24 @@
+import type { DataXY } from 'cheminfo-types';
+
+/**
+ * Convert a flat interleaved array [x, y, x, y, ...] to a DataXY object.
+ * @param data - Flat array alternating x and y values.
+ * @returns DataXY object with separate x and y arrays.
+ */
+export function xyFromInterleaved(
+  data: number[] | Float64Array,
+): DataXY<Float64Array> {
+  if (data.length % 2 !== 0) {
+    throw new RangeError(
+      `xyFromInterleaved: data length must be even, got ${data.length}`,
+    );
+  }
+  const length = data.length / 2;
+  const x = new Float64Array(length);
+  const y = new Float64Array(length);
+  for (let i = 0; i < length; i++) {
+    x[i] = data[2 * i];
+    y[i] = data[2 * i + 1];
+  }
+  return { x, y };
+}
diff --git a/src/xy/xyReduce.ts b/src/xy/xyReduce.ts
index c370786c..9e219adc 100644
--- a/src/xy/xyReduce.ts
+++ b/src/xy/xyReduce.ts
@@ -69,13 +69,14 @@ export function xyReduce(
   const { x, y } = data;
   const {
     from = x[0],
-    to = x.at(-1) as number,
+    to = x.at(-1),
     nbPoints = 4001,
     optimize = false,
   } = options;
   let { zones = [] } = options;
 
   zones = zonesNormalize(zones, { from, to });
+  // @ts-expect-error -- x.at(-1) returns number | undefined but array is guaranteed non-empty here
   if (zones.length === 0) zones = [{ from, to }]; // we take everything
 
   const { internalZones, totalPoints } = getInternalZones(zones, x);
diff --git a/src/xy/xyReduceNonContinuous.ts b/src/xy/xyReduceNonContinuous.ts
index dca47b59..decb38bb 100644
--- a/src/xy/xyReduceNonContinuous.ts
+++ b/src/xy/xyReduceNonContinuous.ts
@@ -51,14 +51,11 @@ export function xyReduceNonContinuous(
     };
   }
   const { x, y } = data;
-  const {
-    from = x[0],
-    to = x.at(-1) as number,
-    maxApproximateNbPoints = 4001,
-  } = options;
+  const { from = x[0], to = x.at(-1), maxApproximateNbPoints = 4001 } = options;
   let { zones = [] } = options;
 
   zones = zonesNormalize(zones, { from, to });
+  // @ts-expect-error -- x.at(-1) returns number | undefined but array is guaranteed non-empty here
   if (zones.length === 0) zones = [{ from, to }]; // we take everything
 
   const { internalZones, totalPoints } = getInternalZones(zones, x);
@@ -68,6 +65,7 @@ export function xyReduceNonContinuous(
     return notEnoughPoints(x, y, internalZones, totalPoints);
   }
 
+  // @ts-expect-error -- x.at(-1) returns number | undefined but array is guaranteed non-empty here
   const deltaX = (to - from) / (maxApproximateNbPoints - 1);
   const newX: number[] = [];
   const newY: number[] = [];
diff --git a/src/xy/xyToInterleaved.ts b/src/xy/xyToInterleaved.ts
new file mode 100644
index 00000000..30330d79
--- /dev/null
+++ b/src/xy/xyToInterleaved.ts
@@ -0,0 +1,19 @@
+import type { DataXY } from 'cheminfo-types';
+
+import { xyCheck } from './xyCheck.ts';
+
+/**
+ * Convert a DataXY object to a flat interleaved array [x, y, x, y, ...].
+ * @param data - DataXY object with x and y arrays.
+ * @returns Flat array alternating x and y values.
+ */
+export function xyToInterleaved(data: DataXY): Float64Array {
+  xyCheck(data);
+  const { x, y } = data;
+  const result = new Float64Array(x.length * 2);
+  for (let i = 0; i < x.length; i++) {
+    result[2 * i] = x[i];
+    result[2 * i + 1] = y[i];
+  }
+  return result;
+}