accumulate simple keys across traces, fixes #974

also, clean-up/clarify the logic

Author: cpsievert

inst/htmlwidgets/plotly.js

@@ -275,29 +275,25 @@ HTMLWidgets.widget({
           continue;
         }
 
+        // set defaults for this keySet
+        // note that we don't track the nested property (yet) since we always 
+        // emit the union -- http://cpsievert.github.io/talks/20161212b/#21
+        keysBySet[trace.set] = keysBySet[trace.set] || {
+          value: [],
+          _isSimpleKey: trace._isSimpleKey
+        };
+        
         // selecting a point of a "simple" trace means: select the 
         // entire key attached to this trace, which is useful for,
         // say clicking on a fitted line to select corresponding observations 
-        if (trace._isSimpleKey) {
-          keysBySet[trace.set] = {value: trace.key, _isSimpleKey: true};
-          // TODO: could this be made more efficient by looping at the trace level first?
-          continue;
-        }
-        
-        // set defaults for this key set
-        keysBySet[trace.set] = keysBySet[trace.set] || 
-          {value: [], _isSimpleKey: false};
-        
-        // the key for this point (could be "nested" -- i.e. a 2D array)
-        var key = trace.key[points[i].pointNumber];
-        if (trace._isNestedKey) {
-          // TODO: is this faster than pushing?
-          keysBySet[trace.set].value = keysBySet[trace.set].value.concat(key);
-        } else {
-          keysBySet[trace.set].value.push(key);
-        }
+        var key = trace._isSimpleKey ? trace.key : trace.key[points[i].pointNumber];
+        // http://stackoverflow.com/questions/10865025/merge-flatten-an-array-of-arrays-in-javascript
+        var keyFlat = trace._isNestedKey ? [].concat.apply([], key) : key;
 
+        // TODO: better to only add new values?
+        keysBySet[trace.set].value = keysBySet[trace.set].value.concat(keyFlat);
       }
+      
       return keysBySet;
     }