title: How to Make a graph with 2 data sets plotted?
body: <p>as of right now I am trying to create a graph, which is fine until I try to add a third column of data on my .csv file. </p>
  
  <p>So essentially I am taking pressure-area isotherms, and what I have been tasked with is to make a pressure, area graph, which I achieved (woot!)</p>
  
  <pre><code>import matplotlib.pyplot as plt
  import numpy as np
  
   x, y = np.loadtxt("Example.csv", delimiter=',', unpack=True)
  plt.plot(x,y)
  plt.xlabel('Area-mm^2')
  plt.ylabel('Pressure mN/m')
  
  plt.title('Pressure-Area Isotherm\nKibron')
  plt.legend()
  plt.show()
  </code></pre>
  
  <p>this is what I got, what I need to do now is to also put the average pixel value of some photos I took into the graph so that I can positively correlate the inverse relation between area and pressure/light intensity.</p>
  
  <p>My.csv (excel file) has three columns if it is not possible to do both of these at the same time could someone show me a way to only pick 2 of the three columns to put on the graph? I.E pressure/area, pressure/pixel values , or area/pixel values. I assume it would involve assigning each column a number(n) and have the pyplot graph "n" vs "n" 
  Edit: I would also like for their to be a second scale so that the overall graph doesn't look wonky . again thanks for the help!</p>
  
  <p>|1st is area |  then pressure| and average pixel value|</p>