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pythonmatplotlibcolormap
Nicolas Martin
Nicolas Martin

Reputation: 595

Pyplot colormap line by line

I'm beginning with plotting on python using the very nice pyplot. I aim at showing the evolution of two series of data along time. Instead of doing a casual plot of data function of time, I'd like to have a scatter plot (data1,data2) where the time component is shown as a color gradient.

In my two column file, the time would be described by the line number. Either written as a 3rd column in the file either using the intrinsic capability of pyplot to get the line number on its own.

Can anyone help me in doing that ?

Thanks a lot.

Nicolas

Upvotes: 2

Views: 9245

Answers (1)

Ffisegydd
Ffisegydd

Reputation: 53698

When plotting using matplotlib.pyplot.scatter you can pass a third array via the keyword argument c. This array can choose the colors that you want your scatter points to be. You then also pick an appropriate colormap from matplotlib.cm and assign that with the cmap keyword argument.

This toy example creates two datasets data1 and data2. It then also creates an array colors, an array of continual values equally spaced between 0 and 1, and with the same length as data1 and data2. It doesn't need to know the "line number", it just needs to know the total number of data points, and then equally spaces the colors.

I've also added a colorbar. You can remove this by removing the plt.colorbar() line.

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


N = 500
data1 = np.random.randn(N)
data2 = np.random.randn(N)
colors = np.linspace(0,1,N)

plt.scatter(data1, data2, c=colors, cmap=cm.Blues)

plt.colorbar()

plt.show()

Example plot

Upvotes: 5

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