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pandas
Kyle
Kyle

Reputation: 283

Pandas: Creating a histogram from string counts

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()

Upvotes: 27

Views: 60003

Answers (4)

Ouyang Ze
Ouyang Ze

Reputation: 490

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

Upvotes: 11

Joe
Joe

Reputation: 776

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.

Upvotes: 63

EdChum
EdChum

Reputation: 394041

You assumed that because your data was composed of strings that calling plot() on this would automatically perform the value_counts() but this is not the case hence the error, all you needed to do was: 

ex3.Severity.value_counts().hist()

Upvotes: 5

Kirell
Kirell

Reputation: 9798

It is a matplotlib issue which cannot order string together, however you can achieve the desired result by labeling the x-ticks:

# emulate your ex3.Severity.value_counts()
data = {'Low': 2, 'Medium': 4, 'High': 5}
df = pd.Series(data)

plt.bar(range(len(df)), df.values, align='center')
plt.xticks(range(len(df)), df.index.values, size='small')
plt.show()

histogram

Upvotes: 8

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