Grouped layers w/ layers not reversed

widget.js

startup: function() {
        this.inherited(arguments);
        NlsStrings.value = this.nls;
        // summary:
        //    this function will be called when widget is started.
        // description:
        //    according to webmap or basemap to create LayerInfos instance
        //    and initialize operLayerInfos;
        //    show layers list;
        //    bind events for layerLis;

        if (this.map.itemId) {
          LayerInfos.getInstance(this.map, this.map.itemInfo)
            .then(lang.hitch(this, function(operLayerInfos) {
              this.operLayerInfos = operLayerInfos;
              
              //begin grouping feature layers for rooms and labels  
              var firstFloorLayers = [], secondFloorLayers = [], thirdFloorLayers = [];  
              array.forEach(this.operLayerInfos.getLayerInfoArray(), function(layerInfo) {  
                //get the original layer title and add it to the new sublayer title  
                layerInfo.layerObject.title = layerInfo.title;  
                if(layerInfo && layerInfo.title.substr(0, 5) === "First"){  
                  firstFloorLayers.push(layerInfo.layerObject);  
                  this.map.removeLayer(layerInfo.layerObject);  
                }  
                if(layerInfo && layerInfo.title.substr(0, 5) === "Secon"){  
                  secondFloorLayers.push(layerInfo.layerObject);  
                  this.map.removeLayer(layerInfo.layerObject);  
                }  
                if(layerInfo && layerInfo.title.substr(0, 5) === "Third"){  
                              thirdFloorLayers.push(layerInfo.layerObject);  
                              this.map.removeLayer(layerInfo.layerObject);  
                            }  
                          }, this);
              //firstFloorLayers.reverse();
              //secondFloorLayers.reverse();
              //thirdFloorLayers.reverse();
                  this.operLayerInfos.addFeatureCollection(firstFloorLayers, "1st Floor");  
                  this.operLayerInfos.addFeatureCollection(secondFloorLayers, "2nd Floor");  
                  this.operLayerInfos.addFeatureCollection(thirdFloorLayers, "3rd Floor");  
                  // end of code to group layers   

                  this.showLayers();
                  this.bindEvents();
                  dom.setSelectable(this.layersSection, false);
                }));
        } else {
          var itemInfo = this._obtainMapLayers();
          LayerInfos.getInstance(this.map, itemInfo)
            .then(lang.hitch(this, function(operLayerInfos) {
              this.operLayerInfos = operLayerInfos;
              this.showLayers();
              this.bindEvents();
              dom.setSelectable(this.layersSection, true);
            }));
        };
          
      },