plotting using color as a gradient in matplotlib

Question

I am new to visualization in python. I am trying to plot the same dataset on the left but by using colors as gradient and gridlines to make it understandable. But I'm stuck and I don't know what I did, I just used the reference codes I got from other similar questions. Can someone help out?

import random
import matplotlib
import matplotlib.pyplot as plt
import tkinter as tk
from matplotlib.widgets import Slider
from matplotlib import colors
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
from matplotlib import style
import numpy as np

style.use('ggplot')
matplotlib.use('TkAgg')

def update(val):
    pos = s_time.val
    ax.axis([pos, pos+10, 20, 40])
    fig.canvas.draw_idle()

def plot():
    canvas = FigureCanvasTkAgg(fig,root)
    canvas.get_tk_widget().pack(side=tk.TOP, fill = tk.BOTH, expand =1)
    
    fig.subplots_adjust(bottom=0.25)

    y_values = [random.randrange(41) for _ in range(40)]
    x_values = [i for i in range(40)]

    ax.axis([0, 9, 20, 40])
    ax.plot(x_values, y_values)

    #cmap = colors.ListedColormap(['red', 'blue','green'])
    #bounds = [0,10,20,30]
    #norm = colors.BoundaryNorm(bounds, cmap.N)
    #ax1.imshow(ax, cmap=cmap, norm=norm)
    im0  = ax1.pcolormesh([x_values,y_values], vmin=0, vmax=1, cmap="RdBu")
    im = fig.colorbar(im0,cax=ax1)
    ax1.grid(which='major', axis='both', linestyle='-', color='white', linewidth=0.5)

    #ax1.set_yticks(np.arange(0, 40, 2.5))

    ax_time = fig.add_axes([0.12, 0.1, 0.78, 0.03])
    return ax_time
    

root = tk.Tk()
fig = plt.Figure(figsize = (10,10),dpi = 150)
ax=fig.add_subplot(121)
ax1=fig.add_subplot(122)
s_time = Slider(plot(), 'Time', 0, 30, valinit=0)
s_time.on_changed(update)
root.mainloop()

The question is not clear and your code doesn’t work. Please specify what you mean by “using colors…to make it understandable”. — Jody Klymak
– Jody Klymak, Commented Dec 7, 2021 at 6:43
I want to make a grid and the points I have given should be plotted on the grid with certain colors. Something like this, matplotlib.org/3.1.1/gallery/images_contours_and_fields/… — sillydoubts
– sillydoubts, Commented Dec 7, 2021 at 6:49
suggest you look at matplotlib.org/stable/gallery/images_contours_and_fields/… instead of that pcolor example. You need, x, y, and a 2-D matrix Z. — Jody Klymak
– Jody Klymak, Commented Dec 7, 2021 at 7:46

Jonathan Weine · Accepted Answer · 2021-12-07 08:29:09Z

0

Disclaimer: Not sure if I understood the question correctly. Maybe you could provide links to the reference questions.

If you want to add a color gradient to a lineplot in matplotlib, to my knowledge the best bet is to use ax.scatter. A similar question was asked here:
Matplotlib: different color for every point of line plot
To mimic the appearance of a lineplot you need to interpolate your data linearly before passing it to the scatter function. The c keyword argument can be used to assign a color-value to each data point and the cmap argument determines the actual mapping from color-value to color.

Here is a minimally working example:

import matplotlib.pyplot as plt
import numpy as np

f, ax = plt.subplots(1, 1)
y_values = np.random.randint(0, 41, size=40)
x_values = np.arange(0, 40, 1)

x_interp = np.arange(0, 40, 0.01)
y_interp = np.interp(x_interp, x_values, y_values)
ax.grid(alpha=0.5)
artist = ax.scatter(x_interp, y_interp, c=y_interp, cmap='seismic', lw=0)
f.colorbar(artist, ax=ax)

Which yields the following plot

EDIT: After clarification I interpret the question as:
"How do I add a background to a lineplot, that shows a color gradient corresponding to the values on the y-axis".

My suggestion is the following:

import matplotlib.pyplot as plt
import numpy as np
f, a  = plt.subplots(1, 1)

value_range = (vmin, vmax) = (0, 40)
x_range = (xmin, xmax) = (0, 60)

X, Y = np.meshgrid(range(xmin, xmax, 1), range(vmin, vmax, 1))
y_data = np.random.randint(vmin, vmax, size=xmax-xmin)
x_data = np.arange(xmin, xmax, 1)

a.pcolormesh(Y, cmap="seismic", alpha=0.5, edgecolors='gray')
a.plot(x_data, y_data, "k-")

Which then yields the following plot

edited Dec 7, 2021 at 8:29

answered Dec 7, 2021 at 6:54

Jonathan Weine

6653 silver badges11 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

sillydoubts Over a year ago

Thanks a lot!! This is similar to what I asked for but I meant colors on a grid Reference graph(Which I want it to look like): matplotlib.org/3.1.1/gallery/images_contours_and_fields/…

Jonathan Weine Over a year ago

If this answers your question, do you mind accepting it as the answer?

Collectives™ on Stack Overflow

plotting using color as a gradient in matplotlib

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related