fetch possible values for gallery view

pdb-js/src/app/visualization-page/visualization-page.component.ts

@@ -90,6 +90,18 @@ export class VisualizationPageComponent implements OnInit {
   dateRangeAsString() : string {
     return (<HTMLInputElement>document.getElementById("search-date-range")).value;
   }
+  
+  gallery(){
+    const that = this;
+    this.plotService.splitQuery(this.query.query, this.splitBy.name).subscribe(function(valuesForSplitBy){
+      console.log("valuesForSplitBy: " + JSON.stringify(valuesForSplitBy));
+      that.plotView.errorMessage = '';
+    },
+    error => {
+      that.plotView.imageUrl = '';
+      that.plotView.errorMessage = error.error.message;
+    });
+  }
     
   plot(){
     const that = this;