rm disable box/violin grouping logic

... and thus allow single-box groups!

Author: etpinard

src/traces/box/cross_trace_calc.js

@@ -73,12 +73,6 @@ function setPositionOffset(traceType, gd, boxList, posAxis) {
     var boxdv = Lib.distinctVals(pointList);
     var dPos0 = boxdv.minDiff / 2;
 
-    // if there's no duplication of x points,
-    // disable 'group' mode by setting counter to 1
-    if(pointList.length === boxdv.vals.length) {
-        fullLayout[numKey] = 1;
-    }
-
     // check for forced minimum dtick
     Axes.minDtick(posAxis, boxdv.minDiff, boxdv.vals[0], true);
 

test/image/baselines/box_single-group.png

@@ -0,0 +1,16 @@
+{
+  "data": [{
+    "type": "box",
+    "x0": 1,
+    "y": [1, 2, 1, 2, 1, 2, 3, 4, 4]
+  }, {
+    "type": "box",
+    "x0": 2,
+    "y": [2, 1, 2, 3, 3, 1, 0, 0, 1]
+  }],
+  "layout": {
+    "title": {"text": "single-box groups!"},
+    "boxmode": "group",
+    "showlegend": false
+  }
+}