want help on heatmap

plz tell me how i place a blank space in heatmap . The dataset contains different group of cluster. suppose first 20 for group1, then 40 for second group , & remaining for group3. I want to draw the heatmap of this dataset having spaces between the groups. Suppose last column of the dataset contains group labels. plz help me. Its urgent. Thanks for your valuable suggestion. i am using guide.