# FAQ: Line Graphs in Matplotlib - Review

This community-built FAQ covers the “Review” exercise from the lesson “Line Graphs in Matplotlib”.

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This exercise can be found in the following Codecademy content:

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Say I have plotted one line for temperature change over time and another for the number of ice cream cones sold over the same time period in the same chart, how can I make use of two different y-axis scales, one on each side of the chart, using matplotlib?

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When I create the lists below, I get the error at the bottom. Why is CodeCademy insisting my data be of equal lengths?

x = list(range(1999, 2010))
y1 = [80, 100, 120, 140]
y2 = [0, 2, 4, 6]

When I Run the code above - ScriptPy returns the following error:
x-values and y-values need to have the same length in order to create ordered pairs of points. `x` has 11 elements and `y1` has 4 elements.

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Hey @array9703050324!

I’m assuming the exercise is using the x list as the x coordinates and y list as the y coordinates. If that’s the case, then the reason the lists must be the same size is because each x coordinate needs a matching y coordinate. And if x has 11 elements and y has four elements, this would not be met

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Steven,

Thank you for the reply. I was attempting to use the data from one of the use cases linked in the lesson. If I were to create this outside of script.py would this work?

I also searched about the same issue, and there seems to be a method `.twinx()`.

``````ax1 = plt.subplot()
ax2 = ax1.twinx()
ax1.plot(x, y1)
ax2.plot(x, y2)
``````
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