fix part 1 of #1978 - keep bin width and trim zeros from 1-bin histograms

Author: alexcjohnson

src/traces/bar/sieve.js

@@ -30,19 +30,26 @@ function Sieve(traces, separateNegativeValues, dontMergeOverlappingData) {
     this.separateNegativeValues = separateNegativeValues;
     this.dontMergeOverlappingData = dontMergeOverlappingData;
 
+    // for single-bin histograms - see histogram/calc
+    var width1 = Infinity;
+
     var positions = [];
     for(var i = 0; i < traces.length; i++) {
         var trace = traces[i];
         for(var j = 0; j < trace.length; j++) {
             var bar = trace[j];
             if(bar.p !== BADNUM) positions.push(bar.p);
         }
+        if(trace[0] && trace[0].width1) {
+            width1 = Math.min(trace[0].width1, width1);
+        }
     }
     this.positions = positions;
 
-    var dv = Lib.distinctVals(this.positions);
+    var dv = Lib.distinctVals(positions);
     this.distinctPositions = dv.vals;
-    this.minDiff = dv.minDiff;
+    if(dv.vals.length === 1 && width1) this.minDiff = width1;
+    else this.minDiff = Math.min(dv.minDiff, width1);
 
     this.binWidth = this.minDiff;
 

src/traces/histogram/calc.js

@@ -135,7 +135,7 @@ module.exports = function calc(gd, trace) {
             break;
         }
     }
-    for(i = seriesLen - 1; i > firstNonzero; i--) {
+    for(i = seriesLen - 1; i >= firstNonzero; i--) {
         if(size[i]) {
             lastNonzero = i;
             break;
@@ -149,6 +149,12 @@ module.exports = function calc(gd, trace) {
         }
     }
 
+    if(cd.length === 1) {
+        // when we collapse to a single bin, calcdata no longer describes bin size
+        // so we need to explicitly specify it
+        cd[0].width1 = Axes.tickIncrement(cd[0].p, binSpec.size, false, calendar) - cd[0].p;
+    }
+
     arraysToCalcdata(cd, trace);
 
     return cd;

test/jasmine/tests/histogram_test.js

@@ -269,6 +269,17 @@ describe('Test histogram', function() {
             expect(out.length).toEqual(9001);
         });
 
+        it('handles single-bin data without extra bins', function() {
+            var out = _calc({
+                x: [2.1, 3, 3.9],
+                xbins: {start: 0, end: 10, size: 2}
+            });
+
+            expect(out).toEqual([
+                {b: 0, p: 3, s: 3, width1: 2}
+            ]);
+        });
+
         function calcPositions(opts, extraTraces) {
             return _calc(opts, extraTraces).map(function(v) { return v.p; });
         }
@@ -554,5 +565,18 @@ describe('Test histogram', function() {
             .catch(fail)
             .then(done);
         });
+
+        it('give the right bar width for single-bin histograms', function(done) {
+            Plotly.newPlot(gd, [{
+                type: 'histogram',
+                x: [3, 3, 3],
+                xbins: {start: 0, end: 10, size: 2}
+            }])
+            .then(function() {
+                expect(gd._fullLayout.xaxis.range).toBeCloseToArray([2, 4], 3);
+            })
+            .catch(fail)
+            .then(done);
+        });
     });
 });