Plotting a horizontal line on multiple subplots in python using pyplot

Question

I am plotting three subplots on the same page. I want to draw a horiZontal line through all the subplots. Following is my code and the resultant graph: (You can notice I can get the horizontal line on one of the plots, but not all)

gs1 = gridspec.GridSpec(8, 2)
gs1.update(left=0.12, right=.94, wspace=0.12)
ax1 = plt.subplot(gs1[0:2, :])
ax2 = plt.subplot(gs1[3:5, :], sharey=ax1)
ax3 = plt.subplot(gs1[6:8, :], sharey=ax1)

ax1.scatter(theta_cord, density, c = 'r', marker= '1')
ax2.scatter(phi_cord, density, c = 'r', marker= '1')
ax3.scatter(r_cord, density, c = 'r', marker= '1')
ax1.set_xlabel('Theta (radians)')
ax1.set_ylabel('Galaxy count')
ax2.set_xlabel('Phi (radians)')
ax2.set_ylabel('Galaxy count')
ax3.set_xlabel('Distance (Mpc)')
ax3.set_ylabel('Galaxy count')
plt.ylim((0,0.004))
loc = plticker.MultipleLocator(base=0.001)
ax1.yaxis.set_major_locator(loc)

plt.axhline(y=0.002, xmin=0, xmax=1, hold=None)

plt.show()

This generates the following:

Again, I want the line I drew on the last subplot to appear on the first two subplots too. How do I do that?

Answer 1

I found a way to do it for anyone who stumbles on this anyways.

We need to replace the following line from the OP:

plt.axhline(y=0.002, xmin=0, xmax=1, hold=None)

We replace it with:

ax1.axhline(y=0.002,xmin=0,xmax=3,c="blue",linewidth=0.5,zorder=0)
ax2.axhline(y=0.002,xmin=0,xmax=3,c="blue",linewidth=0.5,zorder=0)
ax3.axhline(y=0.002,xmin=0,xmax=3,c="blue",linewidth=0.5,zorder=0)

This produces:

Answer 2

Since you have defined ax1 , ax2 and ax3 , it is easy to draw horizontal lines on them. You need to do it separately for them. But your code could be simplified:

for ax in [ax1, ax2, ax3]:
    ax.axhline(y=0.002, c="blue",linewidth=0.5,zorder=0)

According to axhline documentation , xmin and xmax should be in the range (0,1). There is no chance that xmax=3.0 . Since your intent is to draw horizontal line across the axes (which is the default behavior of axhline method ), you can just omit the xmin and xmax parameter.