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pythonnumpymatplotlibplotpolar-coordinates

How can I overlay graphs in matplotlib?

I have created rings using bar graphs and the polar projection of matplotlib.

Now I would like to plot single data points onto these rings. This works fine using plt.plot

Furthermore, I would like to color code the data points based on categories of a different column of the source data. This would work fine using for example ax.scatter(df[xcol], df[ycol], c=df.Color)

However, if I use the scatterfunction, the plotted dots do not overlay with the bar graphs. This only works with the plotfunction.

Does anyone know how I could solve this problem?

This is my current code:


import numpy as np
import matplotlib.pyplot as plt

# draw 4 rings
#Create plot with polar projection for circle structure
fig, ax = plt.subplots(figsize=(12, 8),
                       subplot_kw=dict(projection='polar'))

# remove axes from plot
plt.axis('off')
# create ring coordinates
theta = np.linspace(0, 2 * np.pi, 768)
r = np.linspace(4, 16, 4)
r_ring1 = r[3]-(r[3]-r[2])/2
r_ring2 = r[2]-(r[2]-r[1])/2
r_ring3 = r[1]-(r[1]-r[0])/2
r_ring4 = r[0]/2


# plot the 4 rings
for i in range(r.shape[0]):
    ax.plot(theta, np.repeat(r[i], theta.shape), '-k', lw=1)

#fill rings with radial bar plots
ax.barh(r_ring4, np.pi *2,  height=r[0], color='#ff46a6')
ax.barh(r_ring3, np.pi *2,  height=r_ring2-r_ring3, color='#aaeb8f')
ax.barh(r_ring2, np.pi *2,  height=r_ring2-r_ring3, color='#a2c4c9')
ax.barh(r_ring1, np.pi *2,  height=r_ring1-r_ring2, color='#5DADE2')

#plotting single data points with plot works
for i in range(5):
    plt.plot(0.15*np.pi+i, r_ring1-0.2, marker='o', markersize=7.0, markeredgewidth=1.5,
                 markerfacecolor='red', markeredgecolor='white')

# plotting with scatter is only visible if ax.barh(r_ring2,...) is removed 
for i in range(5):
    ax.scatter(0.15*np.pi+i, r_ring2-0.2, c='red' )
plt.show()

Resulting in the following image: enter image description here

Solution

  • Just use the argument zorder

    import matplotlib.pyplot as plt

# draw 4 rings
#Create plot with polar projection for circle structure
fig, ax = plt.subplots(figsize=(12, 8),
                       subplot_kw=dict(projection='polar'))

# remove axes from plot
plt.axis('off')
# create ring coordinates
theta = np.linspace(0, 2 * np.pi, 768)
r = np.linspace(4, 16, 4)
r_ring1 = r[3]-(r[3]-r[2])/2
r_ring2 = r[2]-(r[2]-r[1])/2
r_ring3 = r[1]-(r[1]-r[0])/2
r_ring4 = r[0]/2


# plot the 4 rings
for i in range(r.shape[0]):
    ax.plot(theta, np.repeat(r[i], theta.shape), '-k', lw=1)

#fill rings with radial bar plots
ax.barh(r_ring4, np.pi *2,  height=r[0], color='#ff46a6', zorder=0)
ax.barh(r_ring3, np.pi *2,  height=r_ring2-r_ring3, color='#aaeb8f', zorder=0)
ax.barh(r_ring2, np.pi *2,  height=r_ring2-r_ring3, color='#a2c4c9', zorder=0)
ax.barh(r_ring1, np.pi *2,  height=r_ring1-r_ring2, color='#5DADE2', zorder=0)

#plotting single data points with plot works
for i in range(5):
    plt.plot(0.15*np.pi+i, r_ring1-0.2, marker='o', markersize=7.0, markeredgewidth=1.5,
                 markerfacecolor='red', markeredgecolor='white')

# plotting with scatter is only visible if ax.barh(r_ring2,...) is removed 
for i in range(5):
    ax.scatter(0.15*np.pi+i, r_ring2-0.2, c='black', zorder=1)
plt.show()

    enter image description here