Add arrayOk for ticklabelindex, add test case to mock

Author: my-tien

src/plots/cartesian/axes.js

@@ -911,7 +911,8 @@ axes.calcTicks = function calcTicks(ax, opts) {
     var ticklabelstep = ax.ticklabelstep;
     var isPeriod = ax.ticklabelmode === 'period';
     var isReversed = ax.range[0] > ax.range[1];
-    var ticklabelIndex = ax.ticklabelindex;
+    var ticklabelIndex = (Array.isArray(ax.ticklabelindex) || !ax.ticklabelindex) ?
+        ax.ticklabelindex : [ax.ticklabelindex];
     var rng = Lib.simpleMap(ax.range, ax.r2l, undefined, undefined, opts);
     var axrev = (rng[1] < rng[0]);
     var minRange = Math.min(rng[0], rng[1]);
@@ -1117,11 +1118,17 @@ axes.calcTicks = function calcTicks(ax, opts) {
             })
             .filter(function(index) { return index !== null; });
 
+        var uniqueIndices = []; // ensure that each label is only drawn once
         majorTickIndices.forEach(function(majorIdx) {
-            var minorIdx = majorIdx + ticklabelIndex;
-            if(minorIdx >= 0 && minorIdx < allTickVals.length) {
-                labelTickVals.push(allTickVals[minorIdx]);
-            }
+            ticklabelIndex.map(function(nextLabelIdx) {
+                var minorIdx = majorIdx + nextLabelIdx;
+                if(uniqueIndices.indexOf(minorIdx) === -1) {
+                    uniqueIndices.push(minorIdx);
+                    if(minorIdx >= 0 && minorIdx < allTickVals.length) {
+                        labelTickVals.push(allTickVals[minorIdx]);
+                    }
+                }
+            });
         });
     }
 

src/plots/cartesian/layout_attributes.js

@@ -722,8 +722,8 @@ module.exports = {
         ].join(' ')
     },
     ticklabelindex: {
-        // In the future maybe add `arrayOk: true` for labeling several minor ticks, e.g. [-1, 0, 1]
         valType: 'integer',
+        arrayOk: true,
         editType: 'calc',
         description: [
             'Only for axes with `type` *date* or *linear*.',

test/image/mocks/zzz_ticklabelindex.json

@@ -164,7 +164,7 @@
     },
     "xaxis2": {
       "title": {
-        "text": "xaxis2: Period before each major tick is labeled"
+        "text": "xaxis2: Period before, after each major tick and in the center between major ticks are labeled"
       },
       "dtick": "M12",
       "minor": {
@@ -175,7 +175,7 @@
       },
       "tickformat": "%b %Y",
       "autorange": "reversed",
-      "ticklabelindex": -1,
+      "ticklabelindex": [-1, 0, 6],
       "tickangle": 90,
       "ticklabelmode": "period",
       "ticklen": 18,

test/plot-schema.json

@@ -15117,10 +15117,16 @@
      "role": "object"
     },
     "ticklabelindex": {
+     "arrayOk": true,
      "description": "Only for axes with `type` *date* or *linear*. Instead of drawing the major tick label, draw the label for the minor tick that is n positions away from the major tick. E.g. to always draw the label for the minor tick before each major tick, choose `ticklabelindex` -1",
      "editType": "calc",
      "valType": "integer"
     },
+    "ticklabelindexsrc": {
+     "description": "Sets the source reference on Chart Studio Cloud for `ticklabelindex`.",
+     "editType": "none",
+     "valType": "string"
+    },
     "ticklabelmode": {
      "description": "Determines where tick labels are drawn with respect to their corresponding ticks and grid lines. Only has an effect for axes of `type` *date* When set to *period*, tick labels are drawn in the middle of the period between ticks.",
      "dflt": "instant",
@@ -16443,10 +16449,16 @@
      "role": "object"
     },
     "ticklabelindex": {
+     "arrayOk": true,
      "description": "Only for axes with `type` *date* or *linear*. Instead of drawing the major tick label, draw the label for the minor tick that is n positions away from the major tick. E.g. to always draw the label for the minor tick before each major tick, choose `ticklabelindex` -1",
      "editType": "calc",
      "valType": "integer"
     },
+    "ticklabelindexsrc": {
+     "description": "Sets the source reference on Chart Studio Cloud for `ticklabelindex`.",
+     "editType": "none",
+     "valType": "string"
+    },
     "ticklabelmode": {
      "description": "Determines where tick labels are drawn with respect to their corresponding ticks and grid lines. Only has an effect for axes of `type` *date* When set to *period*, tick labels are drawn in the middle of the period between ticks.",
      "dflt": "instant",