From 764608a21857125173b3ac09134fee8522dfde80 Mon Sep 17 00:00:00 2001
From: Luc Patiny <luc@patiny.com>
Date: Thu, 3 Sep 2026 12:13:31 +0200
Subject: [PATCH] perf: optimize getSlots

---
 src/xyArray/utils/getSlots.ts | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/xyArray/utils/getSlots.ts b/src/xyArray/utils/getSlots.ts
index c64f78340..4c181f121 100644
--- a/src/xyArray/utils/getSlots.ts
+++ b/src/xyArray/utils/getSlots.ts
@@ -28,10 +28,7 @@ export function getSlots(
   const { delta = 1 } = options;
   const deltaIsFunction = typeof delta === 'function';
 
-  const possibleXs = Float64Array.from(
-    data.flatMap((spectrum) => spectrum.x as number[]),
-  );
-  possibleXs.sort();
+  const possibleXs = sortedXs(data);
 
   if (possibleXs.length === 0) {
     throw new Error('can not process empty arrays');
@@ -65,3 +62,24 @@ export function getSlots(
   }
   return slots;
 }
+
+/**
+ * Fast way of combining array using typed array and set
+ * @param data - The spectra.
+ * @returns Their x values, ascending.
+ */
+function sortedXs(data: DataXY[]): Float64Array {
+  let total = 0;
+  for (const spectrum of data) {
+    total += spectrum.x.length;
+  }
+
+  const possibleXs = new Float64Array(total);
+  let at = 0;
+  for (const spectrum of data) {
+    possibleXs.set(spectrum.x, at);
+    at += spectrum.x.length;
+  }
+  possibleXs.sort();
+  return possibleXs;
+}