fix single-value overlay w/ bingroup edge cases

Author: etpinard

src/traces/histogram/calc.js

@@ -291,9 +291,6 @@ function calcAllAutoBins(gd, trace, pa, mainData, _overlayEdgeCase) {
             }
         }
 
-        // TODO how does work with bingroup ????
-        // - https://github.com/plotly/plotly.js/issues/3881
-        //
         // Edge case: single-valued histogram overlaying others
         // Use them all together to calculate the bin size for the single-valued one
         if(isOverlay && !Registry.traceIs(trace, '2dMap') && newBinSpec._dataSpan === 0 &&
@@ -410,11 +407,15 @@ function handleSingleValueOverlays(gd, trace, pa, mainData, binAttr) {
     // - single-valued traces
     for(i = 0; i < overlaidTraceGroup.length; i++) {
         tracei = overlaidTraceGroup[i];
-        if(tracei === trace) pastThisTrace = true;
-        else if(!pastThisTrace) {
-            // This trace has already had its autobins calculated
-            // (so must not have been single-valued).
-            minSize = Math.min(minSize, tracei[binAttr].size);
+
+        if(tracei === trace) {
+            pastThisTrace = true;
+        } else if(!pastThisTrace) {
+            // This trace has already had its autobins calculated, so either:
+            // - it is part of a bingroup
+            // - it is NOT a single-valued trace
+            binOpts = fullLayout._histogramBinOpts[tracei['_' + mainData + 'bingroup']];
+            minSize = Math.min(minSize, binOpts.size || tracei[binAttr].size);
         } else {
             var resulti = calcAllAutoBins(gd, tracei, pa, mainData, true);
             var binSpeci = resulti[0];

test/jasmine/tests/histogram_test.js

@@ -1,4 +1,5 @@
 var Plotly = require('@lib/index');
+var Plots = require('@src/plots/plots');
 var Lib = require('@src/lib');
 var setConvert = require('@src/plots/cartesian/set_convert');
 
@@ -760,6 +761,60 @@ describe('Test histogram', function() {
             ]);
         });
 
+        // from issue #3881
+        it('handle single-value edge case 1', function() {
+            var gd = {
+                data: [
+                    {uid: 'a', type: 'histogram', y: [1]},
+                    {uid: 'b', type: 'histogram', y: [2]},
+
+                    {uid: 'c', type: 'histogram', y: [1], xaxis: 'x2'},
+                    {uid: 'd', type: 'histogram', y: [3], xaxis: 'x2'},
+
+                    {uid: 'e', type: 'histogram', y: [3]},
+                    {uid: 'f', type: 'histogram', y: [2], xaxis: 'x2'},
+
+                    {uid: 'g', type: 'histogram', x: [1]},
+                    {uid: 'h', type: 'histogram', x: [2], yaxis: 'y2'},
+                    {uid: 'i', type: 'histogram', x: [2]}
+                ],
+                layout: {barmode: 'overlay'}
+            };
+            supplyAllDefaults(gd);
+            Plots.doCalcdata(gd);
+
+            var allBinOpts = gd._fullLayout._histogramBinOpts;
+            var groups = Object.keys(allBinOpts);
+            expect(groups).toEqual(
+                ['a__y', 'b__y', 'c__y', 'd__y', 'e__y', 'f__y', 'g__x', 'h__x', 'i__x'],
+                'bin groups'
+            );
+        });
+
+        // from issue #3881
+        it('handle single-value edge case 2', function() {
+            var gd = {
+                data: [
+                    {bingroup: '1', type: 'histogram', y: [1]},
+                    {uid: 'b', type: 'histogram', y: [2]},
+                    {bingroup: '2', type: 'histogram', y: [1], xaxis: 'x2'},
+                    {bingroup: '1', type: 'histogram', y: [3], xaxis: 'x2'},
+                    {bingroup: '2', type: 'histogram', y: [3]},
+                    {uid: 'f', type: 'histogram', y: [2], xaxis: 'x2'},
+                    {bingroup: '3', type: 'histogram', x: [1]},
+                    {bingroup: '1', type: 'histogram', x: [2], yaxis: 'y2'},
+                    {bingroup: '3', type: 'histogram', x: [2]}
+                ],
+                layout: {barmode: 'overlay'}
+            };
+            supplyAllDefaults(gd);
+            Plots.doCalcdata(gd);
+
+            var allBinOpts = gd._fullLayout._histogramBinOpts;
+            var groups = Object.keys(allBinOpts);
+            expect(groups).toEqual(['1', '2', '3', 'b__y', 'f__y'], 'bin groups');
+        });
+
         function calcPositions(opts, extraTraces, prepend) {
             return _calc(opts, extraTraces, {}, prepend).map(function(v) { return v.p; });
         }