This sample demonstrates how to group data in Listbox and enable group items selectable.
More details about GroupModel, please refer to Developer's Reference

<div apply="org.zkoss.bind.BindComposer" viewModel="@id('vm') @init('demo.listbox.list_group.ListGroupViewModel')">
	<listbox model="@load(vm.groupModel)" height="400px" checkmark="true" 
		onSelect="@command('selectGroup', data=event.reference.value)" multiple="true"
		itemRenderer="demo.listbox.list_group.FoodListGroupRenderer">
		<!-- Make Grouping item selectable-->
		<custom-attributes org.zkoss.zul.listbox.groupSelect="true" />
		<listhead>		
            <listheader width="160px" sort="auto(Category)" label="Category" />
            <listheader width="140px" sort="auto(Name)" label="Name" />
            <listheader hflex="1" sort="auto(TopNutrients)" label="Top Nutrients" />
            <listheader hflex="1" align="center" sort="auto(DailyPercent)" label="% of Daily" />
            <listheader hflex="1" align="center" sort="auto(Calories)" label="Calories" />
            <listheader width="140px" sort="auto(Quantity)" label="Quantity" />        
        </listhead>		
	</listbox>
</div>

package demo.listbox.list_group;

import org.zkoss.zul.Label;
import org.zkoss.zul.Listcell;
import org.zkoss.zul.Listgroup;
import org.zkoss.zul.Listgroupfoot;
import org.zkoss.zul.Listitem;
import org.zkoss.zul.ListitemRenderer;

import demo.data.pojo.Food;

public class FoodListGroupRenderer implements ListitemRenderer<Object> {

	@Override
	public void render(Listitem listitem, Object obj, int index) throws Exception {

		if (listitem instanceof Listgroup) {
			FoodGroupsModel.FoodGroupInfo groupInfo = (FoodGroupsModel.FoodGroupInfo) obj;
			Food food = groupInfo.getFirstChild();
			String groupTxt;
			switch (groupInfo.getColIndex()) {
			case 0:
				groupTxt = food.getCategory();
				break;
			case 1:
				groupTxt = food.getName();
				break;
			case 2:
				groupTxt = food.getTopNutrients();
				break;
			case 3:
				groupTxt = food.getDailyPercent().toString();
				break;
			case 4:
				groupTxt = food.getCalories().toString();
				break;
			case 5:
				groupTxt = food.getQuantity();
				break;
			default:
				groupTxt = food.getCategory();
			}
			listitem.appendChild(new Listcell(groupTxt));
			listitem.setValue(obj);
		} else if (listitem instanceof Listgroupfoot) {
			Listcell cell = new Listcell();
			cell.setSclass("foodFooter");
			cell.setSpan(6);
			cell.appendChild(new Label("Total " + obj + " Items"));
			listitem.appendChild(cell);
		} else {
			Food data = (Food) obj;
			listitem.appendChild(new Listcell(data.getCategory()));
			listitem.appendChild(new Listcell(data.getName()));
			listitem.appendChild(new Listcell(data.getTopNutrients()));
			listitem.appendChild(new Listcell(data.getDailyPercent() + ""));
			listitem.appendChild(new Listcell(data.getCalories() + ""));
			listitem.appendChild(new Listcell(data.getQuantity()));
			listitem.setValue(data);
		}

	}

}

package demo.listbox.list_group;

import org.zkoss.bind.annotation.BindingParam;
import org.zkoss.bind.annotation.Command;
import org.zkoss.bind.annotation.Init;

import demo.data.FoodData;
import demo.data.pojo.Food;
import demo.grid.grouping_model.FoodComparator;

public class ListGroupViewModel {

	private FoodGroupsModel groupModel;
	
	@Init
	public void init() {
		groupModel = new FoodGroupsModel(FoodData.getAllFoodsArray(), new FoodComparator());
		groupModel.setMultiple(true);
	}

	public FoodGroupsModel getGroupModel() {
		return groupModel;
	}

	
	@Command("selectGroup")
	public void selectGroup(@BindingParam("data") Object data) {
		if(data instanceof FoodGroupsModel.FoodGroupInfo) {
			FoodGroupsModel.FoodGroupInfo groupInfo = (FoodGroupsModel.FoodGroupInfo)data;
			int groupIndex = groupInfo.getGroupIndex() ;
			int childCount = groupModel.getChildCount(groupIndex);
			boolean added = groupModel.isSelected(groupInfo);
			for(int childIndex = 0; childIndex < childCount; childIndex++) {
				Food food = groupModel.getChild(groupIndex, childIndex);
				if(added) {
					groupModel.addToSelection(food);
				} else {
					groupModel.removeFromSelection(food);
				}
			}
		}
	}
}

package demo.data.pojo;

public class Food {
	private String category;
	private String name;
	private String topNutrients;
	private Integer dailyPercent;
	private Integer calories;
	private String quantity;

	public Food(String category, String name, String topNutrients, 
			Integer dailyPercent, Integer calories, String quantity) {
		this.category = category;
		this.name = name;
		this.topNutrients = topNutrients;
		this.dailyPercent = dailyPercent;
		this.calories = calories;
		this.quantity = quantity;
	}

	public String getCategory() {
		return category;
	}

	public void setCategory(String category) {
		this.category = category;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getTopNutrients() {
		return topNutrients;
	}

	public void setTopNutrients(String topNutrients) {
		this.topNutrients = topNutrients;
	}

	public Integer getDailyPercent() {
		return dailyPercent;
	}

	public void setDailyPercent(Integer dailyPercent) {
		this.dailyPercent = dailyPercent;
	}

	public Integer getCalories() {
		return calories;
	}

	public void setCalories(Integer calories) {
		this.calories = calories;
	}

	public String getQuantity() {
		return quantity;
	}

	public void setQuantity(String quantity) {
		this.quantity = quantity;
	}

}

package demo.data;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import demo.data.pojo.Food;
import demo.grid.data_filter.FoodFilter;

public class FoodData {

	private static List<Food> foods = new ArrayList<Food>();
	static {
		foods.add(new Food("Vegetables", "Asparagus", "Vitamin K", 115, 43, "1 cup - 92 grams"));
		foods.add(new Food("Vegetables", "Beets", "Folate", 33, 74, "1 cup - 170 grams"));
		foods.add(new Food("Vegetables", "Bell peppers", "Vitamin C", 291, 24, "1 cup - 92 grams"));
		foods.add(new Food("Vegetables", "Cauliflower", "Vitamin C", 92, 28, "1 cup - 124 grams"));
		foods.add(new Food("Vegetables", "Eggplant", "Dietary Fiber", 10, 27, "1 cup - 99 grams"));
		foods.add(new Food("Vegetables", "Onions", "Chromium", 21, 60, "1 cup - 160 grams"));
		foods.add(new Food("Vegetables", "Potatoes", "Vitamin C", 26, 132, "1 cup - 122 grams"));
		foods.add(new Food("Vegetables", "Spinach", "Vitamin K", 1110, 41, "1 cup - 180 grams"));
		foods.add(new Food("Vegetables", "Tomatoes", "Vitamin C", 57, 37, "1 cup - 180 grams"));
		foods.add(new Food("Seafood", "Salmon", "Tryptophan", 103, 261, "4 oz - 113.4 grams"));
		foods.add(new Food("Seafood", "Shrimp", "Tryptophan", 103, 112, "4 oz - 113.4 grams"));
		foods.add(new Food("Seafood", "Scallops", "Tryptophan", 81, 151, "4 oz - 113.4 grams"));
		foods.add(new Food("Seafood", "Cod", "Tryptophan", 90, 119, "4 oz - 113.4 grams"));
		foods.add(new Food("Fruits", "Apples", "Manganese", 33, 61, "1 cup - 160 grams"));
		foods.add(new Food("Fruits", "Cantaloupe", "Vitamin C", 112, 56, "1 cup - 160 grams"));
		foods.add(new Food("Fruits", "Grapes", "Manganese", 33, 61, "1 cup - 92 grams"));
		foods.add(new Food("Fruits", "Pineapple", "Manganese", 128, 75, "1 cup - 155 grams"));
		foods.add(new Food("Fruits", "Strawberries", "Vitamin C", 24, 48, "1 cup - 150 grams"));
		foods.add(new Food("Fruits", "Watermelon", "Vitamin C", 24, 48, "1 cup - 152 grams"));
		foods.add(new Food("Poultry & Lean Meats", "Beef, lean organic", "Tryptophan", 112, 240, "4 oz - 113.4 grams"));
		foods.add(new Food("Poultry & Lean Meats", "Lamb", "Tryptophan", 109, 229, "4 oz - 113.4 grams"));
		foods.add(new Food("Poultry & Lean Meats", "Chicken", "Tryptophan", 121, 223, "4 oz - 113.4 grams"));
		foods.add(new Food("Poultry & Lean Meats", "Venison ", "Protein", 69, 179, "4 oz - 113.4 grams"));
		foods.add(new Food("Grains", "Corn ", "Vatamin B1", 24, 177, "1 cup - 164 grams"));
		foods.add(new Food("Grains", "Oats ", "Manganese", 69, 147, "1 cup - 234 grams"));
		foods.add(new Food("Grains", "Barley ", "Dietary Fiber", 54, 270, "1 cup - 200 grams"));
	}

	public static List<Food> getAllFoods() {
		return new ArrayList<Food>(foods);
	}
	public static Food[] getAllFoodsArray() {
		return foods.toArray(new Food[foods.size()]);
	}

	// This Method only used in "Data Filter" Demo
	public static List<Food> getFilterFoods(FoodFilter foodFilter) {
		List<Food> somefoods = new ArrayList<Food>();
		String cat = foodFilter.getCategory().toLowerCase();
		String nm = foodFilter.getName().toLowerCase();
		String nut = foodFilter.getNutrients().toLowerCase();
		
		for (Iterator<Food> i = foods.iterator(); i.hasNext();) {
			Food tmp = i.next();
			if (tmp.getCategory().toLowerCase().contains(cat) &&
				tmp.getName().toLowerCase().contains(nm)  &&
				tmp.getTopNutrients().toLowerCase().contains(nut)) {
				somefoods.add(tmp);
			}
		}
		return somefoods;
	}

	// This Method only used in "Header and footer" Demo
	public static List<Food> getFoodsByCategory(String category) {
		List<Food> somefoods = new ArrayList<Food>();
		for (Iterator<Food> i = foods.iterator(); i.hasNext();) {
			Food tmp = i.next();
			if (tmp.getCategory().equalsIgnoreCase(category)){
				somefoods.add(tmp);
			}
		}
		return somefoods;
	}
}

package demo.grid.grouping_model;

import java.io.Serializable;
import java.util.Comparator;

import org.zkoss.zul.GroupComparator;

import demo.data.pojo.Food;

public class FoodComparator implements Comparator<Food>, GroupComparator<Food>, Serializable {
	private static final long serialVersionUID = 1L;

	public int compare(Food o1, Food o2) {
		return o1.getCategory().compareTo(o2.getCategory().toString());
	}

	public int compareGroup(Food o1, Food o2) {
		if(o1.getCategory().equals(o2.getCategory()))
			return 0;
		else
			return 1;
	}
}

package demo.listbox.list_group;

import java.util.Comparator;

import org.zkoss.zul.GroupsModelArray;

import demo.data.pojo.Food;

public class FoodGroupsModel extends GroupsModelArray<Food, FoodGroupsModel.FoodGroupInfo, Object, Object> {
	private static final long serialVersionUID = 1L;

	public FoodGroupsModel(Food[] data, Comparator<Food> cmpr) {
		super(data, cmpr);
	}

	protected FoodGroupInfo createGroupHead(Food[] groupdata, int index, int col) {
		return new FoodGroupInfo(groupdata[0], index, col);
	}

	protected Object createGroupFoot(Food[] groupdata, int index, int col) {
		// Return the sum number of each group
		return groupdata.length;
	}
	
	public static class FoodGroupInfo {
		private Food firstChild;
		private int groupIndex;
		private int colIndex;
		
		public FoodGroupInfo(Food firstChild, int groupIndex, int colIndex) {
			super();
			this.firstChild = firstChild;
			this.groupIndex = groupIndex;
			this.colIndex = colIndex;
		}
		
		public Food getFirstChild() {
			return firstChild;
		}
		public int getGroupIndex() {
			return groupIndex;
		}
		public int getColIndex() {
			return colIndex;
		}
	}
}