如何在使用MatPlotLib制作的散点图中为不同的点指定不同的颜色？

Question

Using MatPlotLib and Python, I am making a scatter plot of laptops that has cost on the x-axis and rating on the y-axis. The data is now stored in a tab-separated file.

This link describes MatPlotLib scatter plots. http://matplotlib.sourceforge.net/examples/api/unicode_minus.html

Each laptop's brand is Lenova, HP, or Dell. I want to assign different colors for dots representing laptops of each brand. For instance, Dell laptops are marked by a blue point, while Lenova laptops are represented by a red point.

How can I do that?

Answer 1

A better example for you would be the scatter plot example .

In your case, in place of the close array, you want some array of strings that are one of 'r' , 'g' , or 'b' . So if you can read an array of the brands, you can then translate that into an array of those characters. (And I guess you don't want the equivalent of the volume array, which makes the circles different sizes.)

You could translate your brand array to colors with something like

brandcolors = [brand[i].replace('HP','g').replace('Lenovo','r').replace('Dell','b') for i in range(len(brand))]

Then, the plotting function would look like

scatter(cost, rating, c=brandcolors)

Adding a legend gets a little tricky. The matplotlib docs suggest using a "proxy artist", where you create something, but don't put it on the plot. For example:

pr = Rectangle((0, 0), 1, 1, fc='r')
pg = Rectangle((0, 0), 1, 1, fc='g')
pb = Rectangle((0, 0), 1, 1, fc='b')
legend([pr, pg, pb], ['Lenovo', 'HP', 'Dell'])

That's a little ugly because it comes out as a rectangle regardless of the dot shape. The other possible hack is to actually plot a single dot, but make sure it stays off the plot area.

plot([-100], 'ro', label='Lenovo')
...
ax.set_ylim(bottom=0)
legend()