a = pd.Dataframe({"date":days,
                    "store":"a",
                    "sales": np.random.randint(100,200,size=10)})

b = pd.Dataframe({"date":days,
                    "store":"b",
                    "sales": np.random.randint(100,200,size=10)})                    

c = spd.Dataframe({"date":days,
                    "store":"c",
                    "sales": np.random.randint(100,200,size=10)})                    
                    
c = spd.Dataframe({"date":days,
                    "store":"c",
                    "sales": np.random.randint(100,200,size=10)})                    
