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I'm new to python, and was playing around with it's plotting capability. I wanted to plot Y1 and Y2 where X values go from 10 to 100 with steps of 10, and 100 to 10 with steps of -10.

I was able to plot this using Excel. Here are the X and Y values

X  = [10 20 30 40 50 60 70 80 90 100 100 90 80 70 60 50 40 30 20 10]
Y1 = [0 100 200 300 400 500 600 700 800 900 900 800 700 600 500 400 300 200 100 0]
Y2 = [100 200 300 400 500 600 700 800 900 1000 1000 900 800 700 600 500 400 300 200 100]

How do we plot something like this in python using matplotlib and numpy?

tmdavison
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isunny
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  • Unless you're asking someone else to plot the data for you, I don't see a need to dump them here. – nebuch Aug 28 '15 at 05:39
  • It'll be also nice to see what have you tried so far. – beezz Aug 28 '15 at 05:40
  • nebuch- I just wanted to be as clear as possible. It's actually hard to explain this in words, and thus I created a sample data set in excel – isunny Aug 28 '15 at 05:47
  • Please share some code what you have tried so that people have better understanding. – Mithlesh Kumar Aug 28 '15 at 06:26
  • I don't see what's difficult here, just use a scatter plot for both data series as demonstrated in this answer http://stackoverflow.com/a/4270437/1093485 – Bas Jansen Aug 28 '15 at 07:25

2 Answers2

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Its unclear exactly what you are asking. Do you want the repeated X values to plot on top of each other? In which case, you can use ax.plot as shown in the first example (ax1) below.

If you want the X axis to show all the X values in the order they appear in your list, you could use scatter, then just set the xticklabels to the values in X, as shown in the second example below (ax2)

As stated above in comments, neither of these are particularly difficult: there are lots of examples in the matplotlib gallery.

import matplotlib.pyplot as plt

X  = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10]
Y1 = [0, 100, 200, 300, 400, 500, 600, 700, 800, 900, 900, 800, 700, 600, 500, 400, 300, 200, 100, 0]
Y2 = [100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1000, 900, 800, 700, 600, 500, 400, 300, 200, 100]

fig = plt.figure()
ax1=plt.subplot(211)
ax2=plt.subplot(212)

# First example: overlap repeated X values
ax1.plot(X,Y1,'ro')
ax1.plot(X,Y2,'bo')
ax1.set_title('ax.plot')

# Second example: keep all X values in sequential order
ax2.scatter(range(len(Y1)),Y1,color='r')
ax2.scatter(range(len(Y2)),Y2,c='b')
ax2.set_title('ax.scatter')
ax2.set_xlim(0,len(Y1)-1)
ax2.set_xticks(range(len(Y1)))
ax2.set_xticklabels(X)

plt.show()

enter image description here

tmdavison
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Actually you don't HAVE to use numpy to plot with matplotlib. You can use normal python lists for plotting with matplotlib. NumPy is the package for scientific computation with Python. Its used for its great capabilities for handling matrices. Doing the matrix operation with standard lists is slower. That's why numpy is great.

You can read about numpy here!

You can take help from this link for plotting data with pyplot. Tweak around the parameters to see what you find.

Also I am providing this simple code for plotting. I assume you know how to use import in python. 

import matplotlib.pyplot as plt

X = [range(0,100,10)]
Y = [range(0,1000,100)]

plt.scatter(X,Y)
plt.show()

If you insist on using numpy you can change the code of these two portions 

import numpy as np

X = np.array([range(0,100,10)])
Y = np.array([range(0,1000,100)])
Shubhashis
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  • The OP is asking for a single plot to list both his datasets. Therefore, your solution does not work and he will need to use an `axes` object. – Bas Jansen Aug 28 '15 at 07:26