diff --git a/src/plots/cartesian/set_convert.js b/src/plots/cartesian/set_convert.js
index 903864504e8..2d7c26cc3f2 100644
--- a/src/plots/cartesian/set_convert.js
+++ b/src/plots/cartesian/set_convert.js
@@ -126,12 +126,20 @@ module.exports = function setConvert(ax, fullLayout) {
      */
     function setCategoryIndex(v) {
         if(v !== null && v !== undefined) {
-            var c = ax._categories.indexOf(v);
-            if(c === -1) {
+            if(ax._categoriesMap === undefined) {
+                ax._categoriesMap = {};
+            }
+
+            if(ax._categoriesMap[v] !== undefined) {
+                return ax._categoriesMap[v];
+            } else {
                 ax._categories.push(v);
-                return ax._categories.length - 1;
+
+                var curLength = ax._categories.length - 1;
+                ax._categoriesMap[v] = curLength;
+
+                return curLength;
             }
-            return c;
         }
         return BADNUM;
     }
@@ -139,9 +147,12 @@ module.exports = function setConvert(ax, fullLayout) {
     function getCategoryIndex(v) {
         // d2l/d2c variant that that won't add categories but will also
         // allow numbers to be mapped to the linearized axis positions
-        var index = ax._categories.indexOf(v);
-        if(index !== -1) return index;
-        if(typeof v === 'number') return v;
+        if(ax._categoriesMap) {
+            var index = ax._categoriesMap[v];
+            if(index !== undefined) return index;
+        }
+
+        if(typeof v === 'number') { return v; }
     }
 
     function l2p(v) {
@@ -325,6 +336,8 @@ module.exports = function setConvert(ax, fullLayout) {
 
         // TODO cleaner way to handle this case
         if(!ax._categories) ax._categories = [];
+        // Add a map to optimize the performance of category collection
+        if(!ax._categoriesMap) ax._categoriesMap = {};
 
         // make sure we have a domain (pull it in from the axis
         // this one is overlaying if necessary)
diff --git a/src/plots/plots.js b/src/plots/plots.js
index 6f4dfcf913e..d84500bc07b 100644
--- a/src/plots/plots.js
+++ b/src/plots/plots.js
@@ -1950,6 +1950,13 @@ plots.doCalcdata = function(gd, traces) {
     // to be filled in later by ax.d2c
     for(i = 0; i < axList.length; i++) {
         axList[i]._categories = axList[i]._initialCategories.slice();
+
+        // Build the lookup map for initialized categories
+        axList[i]._categoriesMap = {};
+        for(j = 0; j < axList[i]._categories.length; j++) {
+            axList[i]._categoriesMap[axList[i]._categories[j]] = j;
+        }
+
         if(axList[i].type === 'category') hasCategoryAxis = true;
     }
 
@@ -1994,6 +2001,8 @@ plots.doCalcdata = function(gd, traces) {
             axList[i]._min = [];
             axList[i]._max = [];
             axList[i]._categories = [];
+            // Reset the look up map
+            axList[i]._categoriesMap = {};
         }
     }
 
diff --git a/src/traces/scatter/plot.js b/src/traces/scatter/plot.js
index 7da03ffe2fe..8e367807a70 100644
--- a/src/traces/scatter/plot.js
+++ b/src/traces/scatter/plot.js
@@ -51,13 +51,13 @@ module.exports = function plot(gd, plotinfo, cdscatter, transitionOpts, makeOnCo
     // Sort the traces, once created, so that the ordering is preserved even when traces
     // are shown and hidden. This is needed since we're not just wiping everything out
     // and recreating on every update.
-    for(i = 0, uids = []; i < cdscatter.length; i++) {
-        uids[i] = cdscatter[i][0].trace.uid;
+    for(i = 0, uids = {}; i < cdscatter.length; i++) {
+        uids[cdscatter[i][0].trace.uid] = i;
     }
 
     scatterlayer.selectAll('g.trace').sort(function(a, b) {
-        var idx1 = uids.indexOf(a[0].trace.uid);
-        var idx2 = uids.indexOf(b[0].trace.uid);
+        var idx1 = uids[a[0].trace.uid];
+        var idx2 = uids[b[0].trace.uid];
         return idx1 > idx2 ? 1 : -1;
     });
 
diff --git a/test/jasmine/tests/axes_test.js b/test/jasmine/tests/axes_test.js
index 6f82ef2b067..73c04444b2e 100644
--- a/test/jasmine/tests/axes_test.js
+++ b/test/jasmine/tests/axes_test.js
@@ -1685,6 +1685,7 @@ describe('Test axes', function() {
             var ax = {
                 type: 'category',
                 _categories: ['a', 'b', 'c', 'd'],
+                _categoriesMap: {'a': 0, 'b': 1, 'c': 2, 'd': 3},
                 tickmode: 'array',
                 tickvals: ['a', 1, 1.5, 'c', 2.7, 3, 'e', 4, 5, -2],
                 ticktext: ['A!', 'B?', 'B->C'],
@@ -1804,6 +1805,7 @@ describe('Test axes', function() {
 
         function _autoBin(x, ax, nbins) {
             ax._categories = [];
+            ax._categoriesMap = {};
             Axes.setConvert(ax);
 
             var d = ax.makeCalcdata({ x: x }, 'x');