nyc_restaurants_5.py

f, ax = plt.subplots(figsize=(10,5))

df["YEAR"] = df.GRADE_DATE.dt.year

gb = df[["YEAR", "GRADE","SCORE"]].groupby(["YEAR","GRADE"]).agg("count")
gb["perc"] = gb / gb.sum(level=0)

for year in df.YEAR.unique():
    bottom = 0
    for grade in sorted(df.GRADE.unique()):
        perc = gb[(gb.index.get_level_values(0) == year) & (gb.index.get_level_values(1) == grade)].perc
        if len(perc) > 0:
            perc = perc.values[0]
            ax.bar(year, perc, bottom=bottom, color=colors[grade])
            bottom += perc

ax.legend(sorted(df.GRADE.unique()), bbox_to_anchor=(1.25,1), loc="upper right")
ax.set_title("Ratings over time")