How to plot two list on the same graph with different colors?

How to plot two list on the same graph with different colors? - Printable Version

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How to plot two list on the same graph with different colors? - Alberto - Jul-18-2017

Dear Python Users,

I tried to plot a graph from two lists on the same graph. However, what I get is that two lists are plotted against each other. How can I plot two lists on the same graph, but with different colors?

import matplotlib.pyplot as plt

train_W = [1,2,3,4,5,6]
train_X = [1,2,3,4,5]
train_Y = [10, 20, 30, 40, 50]
train_Z = [10, 20, 30, 40, 50,25]

alpha = float(input("Input alpha: "))

forecast = []


for x in range(0, len(train_X)+1):
    if x==0:
        forecast.append(train_Y[0])
    else:
        forecast.append(alpha*train_Y[x-1] + (1 - alpha) * forecast[x-1])
plt.plot(forecast,train_Z,'g') 
plt.show()

RE: How to plot two list on the same graph with different colors? - MTVDNA - Jul-18-2017

If you submit two arrays as arguments, it is assumed that they are x-coordinates and y-coordinates respectively. If you use only one array, these values will be used as y-coordinates and the x-coordinates will be [0, 1, 2, ...].

You have multiple options to plot more than one function.

You can submit x and y values for each graph you want to plot:

x_list = range(6)
plt.plot(x_list, forecast, x_list, train_W, x_list, train_Z)

The colors of the lines will be different by default, but if you want to set them manually you could do that like this:

plt.plot(x_list, forecast, 'r-.', x_list, train_W, 'bx', x_list, train_Z, 'y')

But imho this code is not very easy to read. (note that 'r-.' means a dashed red line, 'bx' means blue 'x' markers with no line)

Note that the length of the arrays must be equal, or you'll run into e.g.:

Error:
ValueError: x and y must have same first dimension, but have shapes (6,) and (5,)

Also, if you want to apply other keyword arguments to the plot they'll apply to each of those lines:

plt.plot(x_list, forecast, x_list, train_W, x_list, train_Z, label='test')
plt.legend()
plt.show()

Each line in this plot will have the same entry in the in the legend.

That's why I prefer method 2: calling plot() separately for each line:

plt.plot(forecast)
plt.plot(train_Z)
plt.show()

or with x-values explicitly included:

plt.plot(x_list, forecast)
plt.plot(x_list, train_Z)
plt.show()

or with different keyword arguments for each line

plt.plot(x_list, forecast, label='forecast')
plt.plot(x_list, train_Z, label='train Z')
plt.legend()
plt.show()

You can find more info about how to use arguments for plot here: https://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.plot

RE: How to plot two list on the same graph with different colors? - Alberto - Jul-18-2017

Thank you!