dynamicDataTable.setValueExpression("value", FacesContext.getCurrentInstance().getApplication().getExpressionFactory().createValueExpression("#{summaryReportController.sumReports}", String.class));

FacesContext.getCurrentInstance().getApplication().getExpressionFactory().createValueExpression("#{summaryReportController.sumReports}", List.class));

output.setValueExpression("value", FacesContext.getCurrentInstance().getApplication().getExpressionFactory().createValueExpression("#{dynamicItem.expAmount}", Float.class));

<h:datatable binding="#{summaryReportController.dynamicDataTable}" var="dynamicItem" value="#{summaryReportController.sumReports}"/>

private List<SumReport> sumReports;
private String[] summaryTableHeaders;
private HtmlDataTable dynamicDataTable;
private boolean loaded;
private void populateDynamicDataTable(){

for(int i=0; i<sumReports.size();i++){
HtmlColumn column = new HtmlColumn();
dynamicDataTable.getChildren().add(column);

HtmlOutputText header = new HtmlOutputText();
header.setValue(summaryTableHeaders[i]);
column.setHeader(header);

HtmlOutputText output = new HtmlOutputText();
output.setValueExpression("value", FacesContext.getCurrentInstance().getApplication().getExpressionFactory().createValueExpression("#{dynamicItem.expAmount}", Float.class));
column.getChildren().add(output);
}
}

public HtmlPanelGroup getDynamicDataTable(){
if(loaded){
loadDynamicList();
populateDynamicDataTable();
}
return dynamicDataTable;
}

public void setDynamicDataTable(HtmlPanelGroup dynamicDataTable) {
this.dynamicDataTable = dynamicDataTable;
}

public List<SumReport> getSumReports() {
return sumReports;
}

//----------------------Convinience methods for reload dataTable
public boolean isLoaded(){
return loaded;
}
//setLoaded
........
//Call this like actionListener=#{summaryReportController.needReload} when you need reload datatble
public void needReload(){
setLoaded(false);
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Controller {

	private List<String> headers;
	public List<String> getHeaders() {
		if(headers == null){
			headers = new ArrayList<String>();
			Branch branch = getBranches().get(0);
			for(Expense expense : branch.getExpenses()){
				headers.add(expense.getDescription());
			}
		}
		return headers;
	}

	public List<Branch> getBranches() {
		if(branches == null){
			//loadBranches();
		}
		return branches;
	}

	private List<Branch> branches;
	
}

class Branch{
	private String name;
	public String getName() {
		return name;
	}
	public List<Expense> getExpenses() {
		if(expenses == null){
			expenses = Arrays.asList(getExpensesDaoImpl().getExpenses());
		}
		return expenses;
	}

	public float getSumAmount() {
		float sumAmount = 0;
		for(Expense expense: getExpenses()){
			sumAmount += expense.getAmount();
		}
		return sumAmount;
	}
	private List<Expense> expenses;

}

class Expense{
	private float amount;
	private String description;
	public float getAmount() {
		return amount;
	}
	public String getDescription() {
		return description;
	}
}

<h:dataTable value="#{controller.branches}" var="branch">
	<h:column>
		<f:facet name="header" >
			<h:outputText value="Branch name:"/>
		</f:facet>    
		<h:outputText value="#{branch.name}"/>
	</h:column>
	<ui:repeat value="#{branch.expenses}" var="expense">
		<h:column>
			<h:outputText value="#{expense.amount}" />
		</h:column>
	</ui:repeat>
	<h:column>
		<f:facet name="header" >
			<h:outputText value="Total:"/>
		</f:facet>    
		<h:outputText value="#{branch.sumAmount}"/>
	</h:column>
</h:dataTable>