How to add legend to scatter plot that has colour assignment

Question

I have an a list of x and y values and list of colour assignments for each point ('green', 'blue', 'red', etc). All of the examples I have found produce a legend based on separate plt.scatter() commands which later a simple plt.legend() suffices. making matplotlib scatter plots from dataframes in Python's pandas. My scatter does not have separate scatters for each coloured group. So how do I produce a legend that shows the colours of each group?

import matplotlib.pyplot as plt

colors = ["red", "orange", "green", "blue", "purple", "gray"]
regions = ["Hanoi", "Nha Trang", "Vung Tau", "Phu Quoc", "Quang Ngai", "Saigon"]
region_colors=dict(zip(regions,colors))

grp_color=[]
for i in data['Region']:
    grp_color.append(region_colors[i]) 

x_long=data[' Longitude']
y_lat=data[" Latitude"]
plt.scatter(x_long,y_lat,c=grp_color)
plt.legend(grp_color,regions,loc='right')

The logic is reversed here. Usually the easiest way to produce a legend for a scatter plot with different colors is to split the data up, plot different scatter plots (or normal plots) and use `plt.legend()`. — ImportanceOfBeingErnest, Feb 11 '17 at 19:54
so i should go back to the dataframe and split it up so I can plot each group separately? — Spencer Trinh, Feb 11 '17 at 20:01
That certainly is an option. You can also use my answer below. — ImportanceOfBeingErnest, Feb 11 '17 at 20:03

ImportanceOfBeingErnest · Accepted Answer · 2017-02-11T20:21:00.103

2

Assuming you have a list of colors colors = ["blue", "red", "green"] and a list of regions regions = ["Africa", "America", "Australia"] you can create a list of legend handles and use it to create the legend:

handlelist = [plt.plot([], marker="o", ls="", color=color)[0] for color in colors]
plt.legend(handlelist,regions,loc='right')

edited Feb 11 '17 at 20:21

answered Feb 11 '17 at 20:02

ImportanceOfBeingErnest

321,279
53
665
712

thanks for your quick suggestion, I am getting this error message with your code: "ValueError: to_rgba: Invalid rgba arg "Islands" to_rgb: Invalid rgb arg "Islands" could not convert string to float: 'islands'' – Spencer Trinh Feb 11 '17 at 20:08
ok, its because my region_colors is a dictionary, so I replaced region_colors with region_colors.values(). but the legend does not show anything, its just a white square – Spencer Trinh Feb 11 '17 at 20:20
I edited the answer, now it should directly work for you. – ImportanceOfBeingErnest Feb 11 '17 at 20:21
fantastic, it worked. thanks so much! why do we only take the first element of the handlelist? – Spencer Trinh Feb 11 '17 at 20:27
We only take the first element of the list of lines and put it into the `handlelist`. `plt.plot()` returns a list of lines (in this case only one) and we need that item from the list, instead of the list itself. – ImportanceOfBeingErnest Feb 11 '17 at 20:31
i've been looking for this answer for so long, thank you! – Semih Cantürk Dec 22 '20 at 17:55

How to add legend to scatter plot that has colour assignment

1 Answers1

Related