Pandas: Creating a histogram from string counts

Question

I need to create a histogram from a dataframe column that contains the values "Low', 'Medium', or 'High'. When I try to do the usual df.column.hist(), i get the following error.

ex3.Severity.value_counts() Out[85]:  Low       230 Medium     21 High       16 dtype: int64  ex3.Severity.hist()   TypeError                                 Traceback (most recent call last) <ipython-input-86-7c7023aec2e2> in <module>() ----> 1 ex3.Severity.hist()  C:\Users\C06025A\Anaconda\lib\site-packages\pandas\tools\plotting.py in hist_series(self, by, ax, grid, xlabelsize, xrot, ylabelsize, yrot, figsize, bins, **kwds) 2570         values = self.dropna().values 2571  ->2572         ax.hist(values, bins=bins, **kwds) 2573         ax.grid(grid) 2574         axes = np.array([ax])  C:\Users\C06025A\Anaconda\lib\site-packages\matplotlib\axes\_axes.py in hist(self, x, bins, range, normed, weights, cumulative, bottom, histtype, align, orientation, rwidth, log, color, label, stacked, **kwargs) 5620             for xi in x: 5621                 if len(xi) > 0: ->5622                     xmin = min(xmin, xi.min()) 5623                     xmax = max(xmax, xi.max()) 5624             bin_range = (xmin, xmax)  TypeError: unorderable types: str() < float() 

Answer 1

ex3.Severity.value_counts().plot(kind='bar') 

Is what you actually want.

When you do:

ex3.Severity.value_counts().hist() 

it gets the axes the wrong way round i.e. it tries to partition your y axis (counts) into bins, and then plots the number of string labels in each bin.

Answer 2

Just an updated answer (as this comes up a lot.) Pandas has a nice module for styling dataframes in many ways, such as the case mentioned above....

ex3.Severity.value_counts().to_frame().style.bar()

...will print the dataframe with bars built-in (as sparklines, using excel-terminology). Nice for quick analysis on jupyter notebooks.

see pandas styling docs