Fix category init for non-matching axes on graphs with matching axes

src/plots/cartesian/set_convert.js

@@ -575,13 +575,21 @@ module.exports = function setConvert(ax, fullLayout) {
 
     // should skip if not category nor multicategory
     ax.clearCalc = function() {
+        var emptyCategories = function() {
+            ax._categories = [];
+            ax._categoriesMap = {};
+        };
+
         var matchGroups = fullLayout._axisMatchGroups;
 
         if(matchGroups && matchGroups.length) {
+            var found = false;
+
             for(var i = 0; i < matchGroups.length; i++) {
                 var group = matchGroups[i];
 
                 if(group[axId]) {
+                    found = true;
                     var categories = null;
                     var categoriesMap = null;
 
@@ -598,14 +606,14 @@ module.exports = function setConvert(ax, fullLayout) {
                         ax._categories = categories;
                         ax._categoriesMap = categoriesMap;
                     } else {
-                        ax._categories = [];
-                        ax._categoriesMap = {};
+                        emptyCategories();
                     }
+                    break;
                 }
             }
+            if(!found) emptyCategories();
         } else {
-            ax._categories = [];
-            ax._categoriesMap = {};
+            emptyCategories();
         }
 
         if(ax._initialCategories) {

test/image/mocks/axes_matches-linear-categories.json

@@ -0,0 +1,65 @@
+{
+  "data": [
+    {
+      "y": [ "a", "b" ],
+      "x": [ 1, 2 ],
+      "xaxis": "x",
+      "yaxis": "y"
+    },
+    {
+      "y": [ "a", "b" ],
+      "x": [ 1, 2 ],
+      "xaxis": "x2",
+      "yaxis": "y"
+    },
+    {
+      "x": [ "a", "b" ],
+      "y": [ 1, 2 ],
+      "xaxis": "x3",
+      "yaxis": "y2"
+    },
+    {
+      "x": [ "a", "b" ],
+      "y": [ 1, 2 ],
+      "xaxis": "x3",
+      "yaxis": "y3"
+    }
+  ],
+  "layout": {
+    "showlegend": false,
+    "xaxis": {
+      "title": {
+        "text": "matches ->"
+      },
+      "domain": [ 0, 0.5 ]
+    },
+    "xaxis2": {
+      "title": {
+        "text": "matches <-"
+      },
+      "domain": [ 0.5, 1 ],
+      "matches": "x"
+    },
+    "xaxis3": {
+      "anchor": "y2"
+    },
+    "yaxis": {
+      "domain": [ 0, 0.4 ]
+    },
+    "yaxis2": {
+      "title": {
+        "text": "matches<br>->"
+      },
+      "anchor": "x3",
+      "domain": [ 0.5, 0.75 ]
+    },
+    "yaxis3": {
+      "anchor": "x3",
+      "title": {
+        "text": "matches<br><-"
+      },
+      "domain": [ 0.75, 1 ],
+      "matches": "y2"
+    }
+  }
+}