Plotting 2 data sets in 1 graph + linear regression in MATPLOTLIB

Question

I'm new to Python and have any programming background..
I'm trying to plot 2 data sets of y for the same x data set, linear regress it using scipy and get the R^2 value. This is how i've gotten so far:

import matplotlib

import matplotlib.pyplot as pl



from scipy import stats



#first order

'''sin(Δθ)'''

y1 = [-0.040422445,-0.056402365,-0.060758191]

#second order

'''sin(Δθ)'''

y2 = [-0.083967708, -0.107420964, -0.117248521]

''''λ, theo (nm)'''

x= [404.66, 546.07, 579.06]

pl.title('Angular displacements vs. Theoretical wavelength')

pl.xlabel('theoretical λ (in nm)')

pl.y1label('sin(Δθ) of 1st order images')

pl.y2label('sin(Δθ) of 2nd order images')

plot1 = pl.plot(x, y1, 'r')

plot2 = pl.plot(x, y2, 'b')

pl.legend([plot1, plot2], ('1st order images', '2nd order images'), 'best', numpoints=1)

slope1, intercept1, r_value1, p_value1, std_err1 = stats.linregress(x,y1)

slope2, intercept2, r_value2, p_value2, std_err2 = stats.linregress(x,y2)

print "r-squared:", r_value1**2

print "r-squared:", r_value2**2

pl.show()

...i dont' get any plot and i get the error:
"UnicodeDecodeError: 'ascii' codec can't decode byte 0xce in position 12: ordinal not in range(128)"

which i don't understand. can somebody help and tell me what's wrong with my code? thank youuu

Answer 1

There are multiple errors in this code.

You cannot simply type greek letters in plot labels and titles, here is how you can do it:
```
pl.xlabel(r'theoretical $\lambda$ (in nm)')
```
y1label and y2label are not objects of the pl module
In Python, # blah blah is different from '''blah blah'''. The first one is a comment, the second one is an expression. You can assign the second one to a variable (a = '''blah blah''') but you cannot assign the first one to a variable: a = # blah blah yields a SyntaxError.

Here is a code that should work:

import matplotlib
import matplotlib.pyplot as pl
from scipy import stats

y1 = [-0.040422445,-0.056402365,-0.060758191]
y2 = [-0.083967708, -0.107420964, -0.117248521]
x= [404.66, 546.07, 579.06]

pl.title('Angular displacements vs. Theoretical wavelength')
pl.xlabel(r'theoretical $\lambda$ (in nm)')
pl.ylabel(r'sin($\Delta\theta$)')

y1label = '1st order images'
y2label = '2nd order images'

plot1 = pl.plot(x, y1, 'r', label=y1label)
plot2 = pl.plot(x, y2, 'b', label=y2label)

pl.legend()

slope1, intercept1, r_value1, p_value1, std_err1 = stats.linregress(x,y1)
slope2, intercept2, r_value2, p_value2, std_err2 = stats.linregress(x,y2)
print "r-squared:", r_value1**2
print "r-squared:", r_value2**2

pl.show()

Plotting 2 data sets in 1 graph + linear regression in MATPLOTLIB

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