Color matplotlib bar chart based on value

You could use masks for your datasets. A basic example could be the following:

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(10)
y = np.arange(10) * 0.1

mask1 = y < 0.5
mask2 = y >= 0.5

plt.bar(x[mask1], y[mask1], color="red")
plt.bar(x[mask2], y[mask2], color="blue")
plt.show()

The result should be:

UPDATE:

As you updated your question I update the code. For your simple case, and if I understood correctly, you could do the following (ugly) hack:

import pandas as pd

df = pd.DataFrame({'col1':[1,2,3], 'col2':[4,5,6]}, 
                  index = ['row1','row2','row3'])

dfstacked = df.stack()

mask = dfstacked <= 3

colors = np.array(['b']*len(dfstacked))
colors[mask.values] = 'r'

dfstacked.plot(kind = 'bar', rot = 45, color = colors)
plt.show()

Or use a more OO solution.

The code briefly explained:

• I create a mask for my red columns
• I create an array of colors
• Change the the array of colors in order to use other color for my masked values
• As the dfstacked dataframe has a MultiIndex the ticks are not well printed so I use the rot keyword to rotate them. If you want to automate it in order to get a nice plot you can use plt.tight_layout() before plt.show().

I hope it helps.