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I am using matplotlib to plot some data and my code looks like this 

import datetime                                               
import random                                            
import matplotlib.pyplot as plt 
x = [datetime.datetime.strptime(str(i), '%H') for i in range(24)]
# y is an array consists of 8640 elements for 1 day
y = [ 299.8,  299.8,  299.8, ....... 299.7,  299.7,  299.6,  299.6]
# z is an array consists of 144 elements for 1 day
z = [32, 32, 32.3, 33.54, .............31.43, 31.21, 36]

plt.plot(x,y)
plt.plot(x,z)

plt.show

but i get this error. 

ValueError: x and y must have same first dimension

what i understand is that both x and y should equal length. "y" produced data every 10 seconds, so total 8640 points and "z" is the data which is produce every 10 minutes so total points 144. I look at SO and google but could not find to solve my problem. I try this one also 'plotting unix timestamps in matplotlib'

I am new to python and matplotlib. Can someone guide me how to solve this problem and to produce x-axis correctly. Thanks

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    How is that a "weird" error? To make a plot, matplotlib needs to know the x and y coordinate of every point to mark on the axes. If x and y are different lengths, you don't have an (x, y) coordinate pair for every point, so it can't make the plot. You probably need to subsample x to the same time intervals that your y and z arrays are sampled at Commented May 17, 2017 at 14:46
  • @tom subsample but how? . because "y" data points are produced every 10 seconds and "z" are produced every 10 minutes. Can you show me an example. .thanks a lot Commented May 17, 2017 at 14:50
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    plt.plot(x, y) is fine but your x does not make sense. It should contain the timestamp of every element in y. The same goes for plotting z. Here you need a different x with the timestams of the elements in z. Commented May 17, 2017 at 14:59
  • @kazemakase thanks a lot. Can you help me and show an example. my "y" contains 3000 data points for one day and "z" contains 1000 data points. How can I make x accordingly to solve my problem. Commented May 17, 2017 at 15:04
  • @robbin Try the easy way first: xy = np.linspace(0, 1, 3000) and xz = np.linspace(0, 1, 1000). (3000/1000 points seems inconsistent with your question where you state 1000+/500) Commented May 17, 2017 at 15:10

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pandas is pretty handy to tackle dates and ranges of dates:

Get a date range between May 17th 2017 and May 18th 2017, with frequency hours or seconds:

pd.date_range(start='2017 05 17', end='2017 05 18', freq='H')
pd.date_range(start='2017 05 17', end='2017 05 18', freq='s')

or the other option is to start from a certain time, specify the frequency (in this example hours), and the number of periods you need

pd.date_range(start='2017 05 17', periods=15, freq='H')
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3 Comments

I will give it a try and will come back soon. Thanks a lot for the help.
@sorry for late response. I figure it out and for x-axis your answer works well. Thanks .
Good to hear @robbin!

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