violin: defaults to zero width if span is zero

Author: antoinerg

src/traces/violin/calc.js

@@ -37,24 +37,32 @@ module.exports = function calc(gd, trace) {
         var bandwidth = cdi.bandwidth = calcBandwidth(trace, cdi, vals);
         var span = cdi.span = calcSpan(trace, cdi, valAxis, bandwidth);
 
-        // step that well covers the bandwidth and is multiple of span distance
-        var dist = span[1] - span[0];
-        var n = Math.ceil(dist / (bandwidth / 3));
-        var step = dist / n;
-
-        if(!isFinite(step) || !isFinite(n)) {
-            Lib.error('Something went wrong with computing the violin span');
-            cd[0].t.empty = true;
-            return cd;
-        }
-
-        var kde = helpers.makeKDE(cdi, trace, vals);
-        cdi.density = new Array(n);
-
-        for(var k = 0, t = span[0]; t < (span[1] + step / 2); k++, t += step) {
-            var v = kde(t);
-            cdi.density[k] = {v: v, t: t};
-            maxKDE = Math.max(maxKDE, v);
+        if(cdi.min === cdi.max && bandwidth === 0) {
+            // if span is zero and bandwidth is zero, we want a violin with zero width
+            span = cdi.span = [cdi.min, cdi.max];
+            cdi.density = [{v: 1, t: span[0]}];
+            cdi.bandwidth = bandwidth;
+            maxKDE = Math.max(maxKDE, 1);
+        } else {
+            // step that well covers the bandwidth and is multiple of span distance
+            var dist = span[1] - span[0];
+            var n = Math.ceil(dist / (bandwidth / 3));
+            var step = dist / n;
+
+            if(!isFinite(step) || !isFinite(n)) {
+                Lib.error('Something went wrong with computing the violin span');
+                cd[0].t.empty = true;
+                return cd;
+            }
+
+            var kde = helpers.makeKDE(cdi, trace, vals);
+            cdi.density = new Array(n);
+
+            for(var k = 0, t = span[0]; t < (span[1] + step / 2); k++, t += step) {
+                var v = kde(t);
+                cdi.density[k] = {v: v, t: t};
+                maxKDE = Math.max(maxKDE, v);
+            }
         }
 
         maxCount = Math.max(maxCount, vals.length);
@@ -105,8 +113,9 @@ function calcBandwidth(trace, cdi, vals) {
         if(trace.bandwidth) {
             return trace.bandwidth;
         } else {
-            // plot single-value violin with bandwidth of 1
-            return 1;
+            // if span is zero and no bandwidth is specified
+            // it returns zero bandwidth which is a special case
+            return 0;
         }
     }
 

test/image/baselines/violin_only_zeroes.png

@@ -66,6 +66,9 @@
     }
   ],
   "layout": {
+    "template": {
+      "data": {"violin": [{"bandwidth": 1}]}
+    },
     "violinmode": "group",
     "showlegend": false,
     "grid": {

test/image/mocks/violin-offsetgroups.json

@@ -4,15 +4,13 @@
     "y": [0, 0, 0, 0],
     "points": "all",
     "pointpos": 0,
-    "bandwidth": 0.025,
     "meanline": {
       "visible": true
     }
   }, {
     "type": "violin",
     "y": [2, 2, 2, 2],
     "points": "all",
-    "bandwidth": 0.1,
     "pointpos": 0
   }, {
     "type": "violin",

test/image/mocks/violin_only_zeroes.json

@@ -280,7 +280,7 @@ describe('Test violin calc:', function() {
         });
 
         expect(cd.length).toBe(6, '# of violins');
-        expect(cd.every(function(d) { return d.bandwidth; })).toBe(true, 'bandwidth');
+        expect(cd.every(function(d) { return d.bandwidth; })).toBe(false, 'bandwidth');
     });
 
     it('handle multi-value / single-but-unique-value case', function() {
@@ -289,7 +289,7 @@ describe('Test violin calc:', function() {
         });
 
         expect(cd.length).toBe(1, '# of violins');
-        expect(cd[0].bandwidth).toBe(1, 'bandwidth');
+        expect(cd[0].bandwidth).toBe(0, 'bandwidth');
     });
 });