Change color of matplotlib.pyplot points

Question

Here is plot code I've written :

import matplotlib.pyplot as plt

Y = [ 1 , 2 , 3 ]
X = [ 1 , 2 , 4 ]
vocabulary = [1 , 2 , 3]

plt.scatter(X , Y)
for label, x, y in zip(vocabulary, X, Y):
    if(label == 1):
        plt.annotate('', xy=(x, y), xytext=(0, 0), color='red' , textcoords='offset points')
    elif(label == 1):
        plt.annotate('', xy=(x, y), xytext=(0, 0), color='green' , textcoords='offset points')
    elif(label == 1):
        plt.annotate('', xy=(x, y), xytext=(0, 0), color='blue' , textcoords='offset points')
    else :
        plt.annotate('', xy=(x, y), xytext=(0, 0), color='black' , textcoords='offset points')
plt.show()

I'm attempting to change the color depending on the value in array vocabulary if 1 then color the data point red , if 2 then green , if 3 then blue else color the point black. But for all points the color of each point is set to blue. How to color the data point depending on the current value of vocabulary ?

Above code produces :

plasmon360 · Accepted Answer · 2017-04-07 15:55:18Z

6

You could make a dictionary of colors and look it up during scatter plot like shown below

%matplotlib inline
import matplotlib.pyplot as plt

Y = [ 1 , 2 , 3 ,6]
X = [ 1 , 2 , 4 ,5]
vocabulary = [1 , 2 , 3, 0]
my_colors = {1:'red',2:'green',3:'blue'}

for i,j in enumerate(X):
    # look for the color based on vocabulary, if not found in vocubulary, then black is returned.
    plt.scatter(X[i] , Y[i], color = my_colors.get(vocabulary[i], 'black'))

plt.show()

results in

edited Apr 7, 2017 at 15:55

answered Apr 7, 2017 at 15:49

plasmon360

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Comments

Luatic · Accepted Answer · 2017-04-07 15:50:36Z

You just made a little copy & paste error. Just a comment to your style : You could avoid so many ifs when using an list of colors , so :

colors=[red,green,blue,black]

and then :

plt.annotate('', xy=(x, y), xytext=(0, 0), color=colors[max(3,label)] , textcoords='offset points')

Your code has to be so, you always wrote elif label=1, what makes absolutely no sense:

import matplotlib.pyplot as plt

Y = [ 1 , 2 , 3 ]
X = [ 1 , 2 , 4 ]
vocabulary = [1 , 2 , 3]

plt.scatter(X , Y)
for label, x, y in zip(vocabulary, X, Y):
    if(label == 1):
        plt.annotate('', xy=(x, y), xytext=(0, 0), color='red' , textcoords='offset points')
    elif(label == 2):
        plt.annotate('', xy=(x, y), xytext=(0, 0), color='green' , textcoords='offset points')
    elif(label == 3):
        plt.annotate('', xy=(x, y), xytext=(0, 0), color='blue' , textcoords='offset points')
    else :
        plt.annotate('', xy=(x, y), xytext=(0, 0), color='black' , textcoords='offset points')
plt.show()

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