it works! and in element there are no more saving of previous plot

src/tools/pcaplot_tool.js

@@ -294,7 +294,7 @@ morpheus.PcaPlotTool.prototype = {
         var project = this.project;
 
         this.formBuilder.$form.find('[name="draw"]').on('click', function () {
-
+            _this.$chart.empty();
             var colorBy = _this.formBuilder.getValue('color');
             var sizeBy = _this.formBuilder.getValue('size');
             var pc1 = _this.formBuilder.getValue('x-axis');
@@ -315,15 +315,26 @@ morpheus.PcaPlotTool.prototype = {
             console.log(rowIndices);
 
             console.log(colorBy, sizeBy, pc1, pc2);
-            var req = ocpu.call("pcaPlot", {
+            arguments = {
                 es : expressionSet,
-                columns : columnIndices.length > 0 ? columnIndices : null,
-                rows : rowIndices.length > 0 ? rowIndices : null,
                 c1 : pc1,
-                c2 : pc2,
-                colour : colorBy,
-                size : sizeBy
-            }, function (session) {
+                c2 : pc2
+            };
+            if (columnIndices.length > 0) {
+                arguments.columns = columnIndices;
+            }
+            if (rowIndices.length > 0) {
+                arguments.rows = rowIndices;
+            }
+            if (colorBy != "") {
+                arguments.colour = colorBy;
+            }
+            if (sizeBy != "") {
+                arguments.size = sizeBy;
+            }
+
+            console.log(arguments);
+            var req = ocpu.call("pcaPlot", arguments, function (session) {
                 var img = $('<img />', {src : session.getLoc() + 'graphics/1/png'});
                 _this.$chart.prepend(img);
             });