hardmooth
hardmooth

Reputation: 1262

pyplot/matplotlib Bar chart with fill color depending on value

I want to produce in python with matplotlib/pyplot

while keeping module dependencies at a minimum.


Is there something simpler than:

import matplotlib.pyplot as plt

def color_gradient ( val, beg_rgb, end_rgb, val_min = 0, val_max = 1):
    val_scale = (1.0 * val - val_min) / (val_max - val_min)
    return ( beg_rgb[0] + val_scale * (end_rgb[0] - beg_rgb[0]),
             beg_rgb[1] + val_scale * (end_rgb[1] - beg_rgb[1]),
             beg_rgb[2] + val_scale * (end_rgb[2] - beg_rgb[2]))

# -----------------------------------------------
x_lbls = [ "09:00", "09:15", "10:10"]
y_vals = [       7,       9,       5]

plt_idx = np.arange( len( x_lbls))
bar_wd  = 0.35

grad_beg, grad_end = ( 0.5, 0.5, 0.5), (1, 1, 0)
col_list = [ color_gradient( val,
                             grad_beg,
                             grad_end,
                             min( y_vals),
                             max( y_vals)) for val in y_vals]

plt.bar( plt_idx, y_vals, color = col_list)
plt.xticks( plt_idx + bar_wd, x_lbls)
plt.show()

this is still missing the legend color bar


my solution in R with ggplot would be:

library(ggplot2)
df = data.frame( time = 1:10, vals = abs(rnorm( n = 10)))
ggplot( df, aes( x = time, y = vals, fill = vals)) + 
  geom_bar(stat = "identity") + 
  scale_fill_gradient(low="#888888",high="#FFFF00")

and produces the desired output: Example in R with ggplot

Upvotes: 16

Views: 25600

Answers (2)

Nollymar Longa
Nollymar Longa

Reputation: 149

You can use Normalize and ScalarMappable without plotting a scatter. For example:

import matplotlib mpl
import matplotlib.pyplot as plt
from matplotlib import cm

f,(ax1,ax2) = plt.subplots(2)

#ax1 --> plot here your bar chart

norm = mpl.colors.Normalize(vmin=0, vmax=1)

mpl.colorbar.ColorbarBase(ax2, cmap=cm.RdBu,
                                norm=norm,
                                orientation='horizontal')

Finally, add the desired format to the colorbar.

Upvotes: 4

Amy Teegarden
Amy Teegarden

Reputation: 3972

I couldn't figure out how to get the colorbar to work without plotting something else and then clearing it, so it's not the most elegant solution.

import matplotlib.pyplot as plt
from matplotlib import cm
import numpy as np

y = np.array([1, 4, 3, 2, 7, 11])
colors = cm.hsv(y / float(max(y)))
plot = plt.scatter(y, y, c = y, cmap = 'hsv')
plt.clf()
plt.colorbar(plot)
plt.bar(range(len(y)), y, color = colors)
plt.show()

Bar chart with color bar

Upvotes: 22

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