From bbed0ee750e90db0fbd0b8763a80bb309a9c4469 Mon Sep 17 00:00:00 2001
From: kurkle <jukka.kurkela@gmail.com>
Date: Sun, 17 Nov 2019 01:23:16 +0200
Subject: [PATCH 1/2] Cache sorting order of dataset metas

---
 src/core/core.controller.js | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/core/core.controller.js b/src/core/core.controller.js
index a1325394a51..bb0c0cf189f 100644
--- a/src/core/core.controller.js
+++ b/src/core/core.controller.js
@@ -418,6 +418,7 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 		var me = this;
 		var newControllers = [];
 		var datasets = me.data.datasets;
+		var sorted = me._sortedMetasets = [];
 		var i, ilen;
 
 		for (i = 0, ilen = datasets.length; i < ilen; i++) {
@@ -446,8 +447,11 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 				meta.controller = new ControllerClass(me, i);
 				newControllers.push(meta.controller);
 			}
+			sorted.push(meta);
 		}
 
+		sorted.sort(compare2Level('order', 'index'));
+
 		return newControllers;
 	},
 
@@ -727,18 +731,16 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 	 */
 	_getSortedDatasetMetas: function(filterVisible) {
 		var me = this;
-		var datasets = me.data.datasets || [];
+		var metasets = me._sortedMetasets;
 		var result = [];
 		var i, ilen;
 
-		for (i = 0, ilen = datasets.length; i < ilen; ++i) {
+		for (i = 0, ilen = metasets.length; i < ilen; ++i) {
 			if (!filterVisible || me.isDatasetVisible(i)) {
-				result.push(me.getDatasetMeta(i));
+				result.push(metasets[i]);
 			}
 		}
 
-		result.sort(compare2Level('order', 'index'));
-
 		return result;
 	},
 

From a8b976ef7c6955d3593624b52e93c8aa868bc181 Mon Sep 17 00:00:00 2001
From: kurkle <jukka.kurkela@gmail.com>
Date: Mon, 18 Nov 2019 00:00:46 +0200
Subject: [PATCH 2/2] Cache dataset visibility

---
 src/core/core.controller.js | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/src/core/core.controller.js b/src/core/core.controller.js
index bb0c0cf189f..bbb30f662e3 100644
--- a/src/core/core.controller.js
+++ b/src/core/core.controller.js
@@ -434,6 +434,7 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 			meta.order = dataset.order || 0;
 			meta.index = i;
 			meta.label = '' + dataset.label;
+			meta.visible = me.isDatasetVisible(i);
 
 			if (meta.controller) {
 				meta.controller.updateIndex(i);
@@ -707,13 +708,15 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 	 * @private
 	 */
 	transition: function(easingValue) {
-		var me = this;
+		const me = this;
 		var i, ilen;
 
 		if (!me._animationsDisabled) {
-			for (i = 0, ilen = (me.data.datasets || []).length; i < ilen; ++i) {
-				if (me.isDatasetVisible(i)) {
-					me.getDatasetMeta(i).controller.transition(easingValue);
+			const metas = me._getSortedDatasetMetas();
+			for (i = 0, ilen = metas.length; i < ilen; ++i) {
+				let meta = metas[i];
+				if (meta.visible) {
+					meta.controller.transition(easingValue);
 				}
 			}
 		}
@@ -736,8 +739,9 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 		var i, ilen;
 
 		for (i = 0, ilen = metasets.length; i < ilen; ++i) {
-			if (!filterVisible || me.isDatasetVisible(i)) {
-				result.push(metasets[i]);
+			const meta = metasets[i];
+			if (!filterVisible || meta.visible) {
+				result.push(meta);
 			}
 		}
 
@@ -884,13 +888,7 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 	},
 
 	getVisibleDatasetCount: function() {
-		var count = 0;
-		for (var i = 0, ilen = this.data.datasets.length; i < ilen; ++i) {
-			if (this.isDatasetVisible(i)) {
-				count++;
-			}
-		}
-		return count;
+		return this._getSortedVisibleDatasetMetas().length;
 	},
 
 	isDatasetVisible: function(datasetIndex) {