Matplotlib: how to plot data from lists, adding two y-axes?

Question

I need to produce some plots with matplotlib but I am very poor at it. I have five lists which contain 100 values each. Their values vary according to:

I want to be able to produce two line-and-marker charts out of them:

1. The first plot involves List 1, 2, 3, and 4, and has two y-axes. List 1, 2, and 3 rely on the regular y-axis, while list 4 relies on the added y-axis, like the following:

2. The second has to plot just List 4 and 5, but with the regular y-axis.

Do I need to turn the each list into a numpy array before going on? Anyhow, I failed to figure out how to do the plotting with matplotlib. Any help will be much appreciated. Thanks!

Answer 1

You just need to make a twinx axes to plot list 4 on a separate y axis. You can see an example here.

And here's a short script to do what you want. No need to convert to numpy arrays in this case.

import matplotlib.pyplot as plt

# Some sample lists
l1 = [0.7,0.8,0.8,0.9,0.8,0.7,0.6,0.9,1.0,0.9]
l2 = [0.2,0.3,0.1,0.0,0.2,0.1,0.3,0.1,0.2,0.1]
l3 = [0.4,0.6,0.4,0.5,0.4,0.5,0.6,0.4,0.5,0.4]

l4 = [78,87,77,65,89,98,74,94,85,73]
l5 = [16,44,14,55,34,36,76,54,43,32]

# Make a figure
fig = plt.figure()

# Make room for legend at bottom
fig.subplots_adjust(bottom=0.2)

# The axes for your lists 1-3
ax1 = fig.add_subplot(211)
# A twin axis for list 4. This shares the x axis, but has a separate y axis
ax2 = ax1.twinx()

# Plot lines 1-3
line1 = ax1.plot(l1,'bo-',label='list 1')
line2 = ax1.plot(l2,'go-',label='list 2')
line3 = ax1.plot(l3,'ro-',label='list 3')

# Plot line 4
line4 = ax2.plot(l4,'yo-',label='list 4')

# Some sensible y limits
ax1.set_ylim(0,1)
ax2.set_ylim(0,100)

# Your second subplot, for lists 4&5
ax3 = fig.add_subplot(212)

# Plot lines 4&5
ax3.plot(l4,'yo-',label='list 4')
line5 = ax3.plot(l5,'mo-',label='list 5')

# To get lines 1-5 on the same legend, we need to 
# gather all the lines together before calling legend
lines = line1+line2+line3+line4+line5
labels = [l.get_label() for l in lines]

# giving loc a tuple in axes-coords. ncol=5 for 5 columns
ax3.legend(lines, labels, loc=(0,-0.4), ncol=5)

ax3.set_xlabel('events')

# Display the figure
plt.show()