importpandasaspdimportmatplotlib.pyplotaspltfig=plt.figure(figsize=(20,10));ax=fig.gca();df=pd.DataFrame({'year':[2018,2018,2018],'month':[1,1,1],'day':[1,2,3],'value':[1,2,3]})df['date']=pd.to_datetime(df[['year','month','day']])ax.bar(df['date'],df['value'],width=10,align='center')

---------------------------------------------------------------------------ValueError                                Traceback (most recent call last)<ipython-input-12-500999fd6ea9> in <module>      8 df['date'] = pd.to_datetime(df[['year', 'month', 'day']])      9 ---> 10 ax.bar(df['date'], df['value'], width=10,align='center')~/matplotlib/lib/matplotlib/__init__.py in inner(ax, data, *args, **kwargs)   1515     def inner(ax, *args, data=None, **kwargs):   1516         if data is None:-> 1517             return func(ax, *map(sanitize_sequence, args), **kwargs)   1518    1519         bound = new_sig.bind(ax, *args, **kwargs)~/matplotlib/lib/matplotlib/axes/_axes.py in bar(self, x, height, width, bottom, align, **kwargs)   2230             x0 = x   2231             x = np.asarray(self.convert_xunits(x))-> 2232             width = self._convert_dx(width, x0, x, self.convert_xunits)   2233             if xerr is not None:   2234                 xerr = self._convert_dx(xerr, x0, x, self.convert_xunits)~/matplotlib/lib/matplotlib/axes/_axes.py in _convert_dx(dx, x0, xconv, convert)   2055                 dx = [dx]   2056                 delist = True-> 2057             dx = [convert(x0 + ddx) - x for ddx in dx]   2058             if delist:   2059                 dx = dx[0]~/matplotlib/lib/matplotlib/axes/_axes.py in <listcomp>(.0)   2055                 dx = [dx]   2056                 delist = True-> 2057             dx = [convert(x0 + ddx) - x for ddx in dx]   2058             if delist:   2059                 dx = dx[0]pandas/_libs/tslibs/timestamps.pyx in pandas._libs.tslibs.timestamps._Timestamp.__add__()ValueError: Cannot add integral value to Timestamp without freq.