Color code of lines based on an array using Matplotlib

Question

I am drawing multiple horizontal and vertical lines using ax.hlines() and ax.vlines() respectively. I want to assign values to these lines using the array P and the order of assignment is presented in the expected output.

import matplotlib as mpl
import matplotlib.pyplot as plt
from matplotlib.patches import Rectangle
import numpy as np

fig,ax = plt.subplots(1)
n=3
for i in range(0,n):
    for j in range(0,n):
        rect = mpl.patches.Rectangle((200+200*i,200+200*j),10*n, 10*n, linewidth=1, edgecolor='black', facecolor='black')
        ax.add_patch(rect)
        ax.hlines(200+200*i+5*n, 200, 200*n, zorder=0)
        ax.vlines(200+200*j+5*n, 200, 200*n, zorder=0)

ax.set_xlim(left = 0, right = 220*n)
ax.set_ylim(bottom = 0, top = 220*n)
plt.show()

#########################################
P=np.array([[1.9],
       [4.9],
       [6.1],
       [8.2],
       [1.8],
       [5.8],
       [9.7],
       [7.3],
       [8.9],
       [2.5],
       [9.9],
       [0.7]])

#########################################

The current output is

The expected output is

The colormap in the expected output is for illustration only. Based on the array P, it will be in the range 0-10 since the min is 0.7 and max is 9.9 — Wiz123
– Wiz123, Commented Jul 14, 2022 at 5:15
You are expecting a square because in your code every edge should be 200. But in your example.jpg, they seems to be not a square. As@Davide_sd said, it's because of overlapping. My code follows your order as you labeled from P[0]-P[11], and solves the overlapping. — x pie
– x pie, Commented Jul 15, 2022 at 2:55

x pie · Accepted Answer · 2022-07-15 07:21:52Z

1

Values bar is added following @Davide_sd.

I'm not sure if this sovles your problem.

import matplotlib as mpl
import matplotlib.pyplot as plt
from matplotlib.patches import Rectangle
import numpy as np
from matplotlib.colors import Normalize
from matplotlib import cm


fig,ax = plt.subplots(1)
n=3

P=np.array([[1.9],
       [4.9],
       [6.1],
       [8.2],
       [1.8],
       [5.8],
       [9.7],
       [7.3],
       [8.9],
       [2.5],
       [9.9],
       [0.7]])

color = cm.get_cmap('Blues')
norm = Normalize(vmin=0, vmax=10)
color_list = []
for i in range(len(P)):
    color_list.append(color(P[i]/10))
print(color_list)
id = 0
for j in range(0, n):
    for k in range(n-1):
        ax.hlines(200+200*(n-j-1)+5*n, 200*(k+1)+5*n, 200*(k+2)+5*n, zorder=0, colors=color_list[id])
        id += 1

    for i in range(0, n):
        rect = mpl.patches.Rectangle((200+200*i, 200+200*j), 10*n, 10*n, linewidth=1, edgecolor='black', facecolor='black')
        ax.add_patch(rect)
        if j < n-1:
            ax.vlines(200+200*i+5*n, 200*(n-1-j)+5*n, 200*(n-j)+5*n, zorder=0, colors=color_list[id])
            id += 1

cb = fig.colorbar(cm.ScalarMappable(cmap=color, norm=norm))
cb.set_label("Values")
ax.set_xlim(left = 0, right = 220*n)
ax.set_ylim(bottom = 0, top = 220*n)
plt.show()

And the ouput is like:

edited Jul 15, 2022 at 7:21

answered Jul 14, 2022 at 5:58

x pie

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7 Comments

Wiz123 Over a year ago

The number of squares is fine now but as I increase n say from 3 to 4, I see 3 vertical lines not appearing at the bottom. I am looking for a generic code which works for many n. For n=4, the shape of P should be (24,1) which means 24 different values for 24 different lines (horizontal and vertical combined).

x pie Over a year ago

Got it, I will update later.

x pie Over a year ago

Try to change "if j <2" to "if j < n-1"，I suppose it will work.

Wiz123 Over a year ago

There's problem with n=4. It makes multiple lines at a time at some places. Instead I want it to take 1 line at a time and pick values according to P.

x pie Over a year ago

Ofcourse you are right. I will update.

|

Davide_sd · Accepted Answer · 2022-07-14 07:41:10Z

You need to use a colormap, Normalize and ScalarMappable in order to create a colorbar.

Here is the procedure:

import matplotlib as mpl
import matplotlib.pyplot as plt
from matplotlib.patches import Rectangle
import matplotlib.cm as cm
from matplotlib.colors import Normalize
import numpy as np

#########################################
P=np.array([[1.9],
       [4.9],
       [6.1],
       [8.2],
       [1.8],
       [5.8],
       [9.7],
       [7.3],
       [8.9],
       [2.5],
       [9.9],
       [0.7]])

#########################################

# normalize the values. Values between 0 and 10 will be
# normalized to values from 0 and 1.
norm = Normalize(vmin=0, vmax=10)
Pnorm = norm(P)
# choose an appropriate colormap
cmap = cm.Blues

fig,ax = plt.subplots(1)
n=3
k = 0
for i in range(0,n):
    for j in range(0,n):
        rect = mpl.patches.Rectangle((200+200*i,200+200*j),10*n, 10*n, linewidth=1, edgecolor='black', facecolor='black')
        ax.add_patch(rect)
        # extract the color from the colormap
        ax.hlines(200+200*i+5*n, 200, 200*n, zorder=0, color=cmap(Pnorm[k]))
        ax.vlines(200+200*j+5*n, 200, 200*n, zorder=0, color=cmap(Pnorm[k]))
        k += 1

cb = fig.colorbar(ScalarMappable(cmap=cmap, norm=norm))
cb.set_label("Values")
ax.set_xlim(left = 0, right = 220*n)
ax.set_ylim(bottom = 0, top = 220*n)
plt.show()

There is a problem with the way you are currently plotting lines, as they are overlapping. You need to fix it!

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