How to plot a scatter plot with its linear regression?

Question

How can I make an estimated line like that using matplotlib.

Graph generated using excel

I have several points and I plotted them using matplotlib using the following code:

import matplotlib.pyplot as plt
for smp, lbl in zip(samples, labels):
    plt.scatter(smp[0], smp[1], marker='*', cl = 'b', s=100, label=lbl)

# set limit, xlabel, ylabel, legend ...
# ...

plt.show()

Thanks,

You should not plot every single point with it's own scatter command. It takes long and if you want to have a legend, you will have an entry for each point. You could use this: x = [value[0] for value in samples] y = [value[1] for value in samples] — MaxNoe
– MaxNoe, Commented Jul 25, 2014 at 10:35

dwitvliet · Accepted Answer · 2014-07-25 17:03:28Z

1

Use polyfit to do linear regression:

import matplotlib.pyplot as plt
from pylab import polyfit, poly1d

x, y = zip(*samples)

fit = polyfit(x, y, 1)
fit_fn = poly1d(fit)
plt.plot(x,y, '*', x, fit_fn(x), 'k')

plt.show()

Example result:

enter image description here

edited Jul 25, 2014 at 17:03

answered Jul 24, 2014 at 20:19

dwitvliet

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3 Comments

Gabriel Over a year ago

I think you just want fit=polyfit(smp[0],smp[1],1) as smp[0] is array like if its the first argument in plt.scatter. or just do x=smp[0]; y=smp[1]

dwitvliet Over a year ago

@Gabriel No, according to the OP's for loop, the sample array would be of the format [[x1, y1], [x2, y2], [x3, y3], ..]. So sorting x and y first (one way of another) seems necessary.

Gabriel Over a year ago

right, I see it now. was expecting multiple items in the legend of the OP plot if that was the case, but realize now that the OP code didn't make that image.

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