Plotting multiple line graphs in matplotlib

Question

I'm using matplotlib to draw line graphs and whenever I try to draw the second line graph, the y-axis gets printed two times.

import matplotlib.pyplot as plt

x = [0, 1, 2, 3, 4, 5]
y1 = ['1000', '13k', '26k', '42k', '60k', '81k']
y2 = ['1000', '13k', '27k', '43k', '63k', '85k']

plt.plot(x, y1)
plt.plot(x, y2, '-.')

plt.xlabel("X-axis data")
plt.ylabel("Y-axis data")
plt.title('multiple plots')
plt.show()

This is the code I'm using, what am I doing wrong.

Output:

Answer 1

Change the two lines:

y1 = ['1000', '13k', '26k', '42k', '60k', '81k']
y2 = ['1000', '13k', '27k', '43k', '63k', '85k']

to

y1 = [1000, 13000, 26000, 42000, 60000, 81000]
y2 = [1000, 13000, 27000, 43000, 63000, 85000]

It consists of two change. First, plot does not plot a string. Second, you change 'k' to multiples of 1000.

Try the following:

import matplotlib.pyplot as plt

x = [0, 1, 2, 3, 4, 5]
y1 = [1000, 13000, 26000, 42000, 60000, 81000]
y2 = [1000, 13000, 27000, 43000, 63000, 85000]

plt.plot(x, y1, label ='y1')
plt.plot(x, y2, '-.', label ='y2')

plt.xlabel("X-axis data")
plt.ylabel("Y-axis data")
plt.legend()
plt.title('multiple plots')
plt.show()

This also adds labels to the lines.

Answer 2

Your y values are strings instead of numbers, matplotlib lets you plot them but there is no "number" scale to the plot so it simply add the new labels (strings like '85k') on top. A simple fix would be to replace the 'k' in all the strings with 'e3' and then cast all the values to a number using float().

import matplotlib.pyplot as plt

x = [0, 1, 2, 3, 4, 5]

y1 = ['1000', '13k', '26k', '42k', '60k', '81k']
y2 = ['1000', '13k', '27k', '43k', '63k', '85k']

Now convert and plot:

plt.plot(x, [float(i.replace('k', 'e3')) for i in y1])
plt.plot(x, [float(i.replace('k', 'e3')) for i in y2], '-.')

plt.xlabel("X-axis data")
plt.ylabel("Y-axis data")
plt.title('multiple plots')
plt.show()

Here I converted the strings just for the purpose of plotting.