Showing two data sets of `ax2.set_xticklabels` in a subplot

Question

I have an upper subplot that shows two data sets: orange and green.

The following code shows the xtick labels of the green data set,

in the ax2 axis of the upper subplot (axis labelled as X2 in the figure):

ind_pos_Pd3 = [0, 4, 8, 12, 16]
axarr[0].set_xticks(X1_green[ind_pos_Pd3])
ax2.set_xticks(X1_green[ind_pos_Pd3])
ax2.set_xticklabels(["%.2f" % i for i in X2_green[ind_pos_Pd3]])

On the contrary, the following code shows the the xtick labels of the orange data set,

in the ax2 axis of the upper subplot (axis labelled as X2 in the figure):

ind_pos_Bd3 = [0, 4, 8, 12, 16, 20, 24, 28, 32]
axarr[0].set_xticks(X1_orange[ind_pos_Bd3])
ax2.set_xticks(X1_orange[ind_pos_Bd3])
ax2.set_xticklabels(["%.2f" % i for i in X2_orange[ind_pos_Bd3]])

Is there a way to "mix" both schemes and achieve a ax2 axis divided into two panels: the "lower panel" is filled with the labels from the green data set, and the "upper panel" is filled with the labels from the orange data set ?

Something like:

I was thinking on this pseudo-code:

ind_pos_Bd3 = [0, 4, 8, 12, 16, 20, 24, 28, 32]
ind_pos_Pd3 = [0, 4, 8, 12, 16]

axarr[0].set_xticks(X1_orange[ind_pos_Bd3])
axarr[0].set_xticks(X1_green[ind_pos_Pd3])

ax2.set_xticks(X1_green[ind_pos_Pd3])

ax2.set_xticklabels(["%.2f \n %.2f" % i for i in zip(X2_orange[ind_pos_Bd3], X1_green[ind_pos_Pd3]])

However, the "%.2f \n %.2f" scheme is not working.

Minimal working example:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker as mtick

X1_orange =  np.array([  10.,     30.1,    50.2,    70.3,    90.4,   110.51,  130.61,  150.71,  170.81,
             190.91,  211.01,  231.11,  251.21, 271.31,  291.41,  311.52,  331.62,  351.72,
             371.82,  391.92,  412.02,  432.12, 452.22,  472.32,  492.42,  512.53,  532.63,
             552.73,  572.83,  592.93,  613.03, 633.13,  653.23])

X2_orange = np.array([ 2.56691976, 2.5781089 , 2.59624855, 2.62275805, 2.64568568, 2.66607658,
           2.6959714 , 2.7231501 , 2.75529391, 2.78894345, 2.81573712, 2.84711104,
           2.88437499, 2.9191375 , 2.95033337, 2.99340594, 3.02206115, 3.06383265,
           3.08649135, 3.12707204, 3.18500195, 3.24240915, 3.25965166, 3.36137181,
           3.35468811, 3.42661704, 3.46254097, 3.61136855, 3.65505401, 3.89043407,
           3.80421353, 3.79380128, 4.01570509])

X1_green = np.array([  10.   , 30.1  , 50.2  , 70.3  , 90.4  , 110.51, 130.61, 150.71,  170.81,
            190.91, 211.01, 231.11, 251.21, 271.31, 291.41, 311.52, 331.62])

X2_green = np.array([ 1.9894731 , 2.00259207, 2.01875725, 2.04333825, 2.07700656, 2.09629866,
           2.14727031, 2.17488234, 2.2499103 , 2.2698862 , 2.31607409, 2.41452705,
           2.50847008, 2.61117044, 2.70657103, 3.25283819, 3.31585812])

Y0_orange = np.array([-1.87483583, -1.82358431, -1.78627169, -1.75242213, -1.7299256 , -1.69363695,
                -1.64623615, -1.59656948, -1.56967972, -1.55058869, -1.51874314, -1.45673839,
                -1.40554361, -1.39904184, -1.35322104, -1.33906865, -1.30865871, -1.28099683,
                -1.24897269, -1.19802619, -1.17268543, -1.13523614, -1.09290541, -1.05642197,
                -1.00189406, -0.95390527, -0.90890049, -0.82522042, -0.76334378, -0.64504498,
                -0.62782754, -0.47358849, -0.49772039])

Y0_green = np.array([-1.97113854, -1.92908192, -1.84404067, -1.75333855, -1.67575628, -1.58010168,
                -1.48746063, -1.40770641, -1.31802444, -1.2302243 , -1.14927205, -1.04251178,
                -0.91661452, -0.82924669, -0.65075739, -0.37715382, -0.21349827])

##### THREE SUBPLOTS::

###### Y0 plot:
f, axarr = plt.subplots(3, sharex=True, figsize=(11,5))
axarr[0].plot(X1_orange, Y0_orange, linestyle='--', marker="o",  markersize=6, color='orange')
axarr[0].plot(X1_green, Y0_green, linestyle='--', marker="o",  markersize=6, color='green')
axarr[0].set_ylabel('Y0', fontsize=15)

# Create a new axis:
axarr[0].grid()
ax2 = axarr[0].twiny()

# Make the ax1-ticks and ax1-tick-labels match the line color (blue):
axarr[0].tick_params('x', colors='blue')

# Make the ax2-ticks and ax2-tick-labels match the red color: 
# this only controls the font and color of label 
ax2.set_xlabel('x2', fontsize=14, color='red')
# this also adds the numbers on top of the tics,
# but sets the colors of the tics
ax2.tick_params('x', colors='orange')

# Set xlimits of ax2 the same as ax1
ax2.set_xlim(axarr[0].get_xlim())

# Set ticks at desired position
ind_pos_Bd3 = [0, 4, 8, 12, 16, 20, 24, 28, 32]
axarr[0].set_xticks(X1_orange[ind_pos_Bd3])
ax2.set_xticks(X1_orange[ind_pos_Bd3])
ax2.set_xticklabels(["%.2f" % i for i in X2_orange[ind_pos_Bd3]])

#ind_pos_Pd3 = [0, 4, 8, 12, 16]
#axarr[0].set_xticks(X1_green[ind_pos_Pd3])
#ax2.set_xticks(X1_green[ind_pos_Pd3])
#ax2.set_xticklabels(["%.2f" % i for i in X2_green[ind_pos_Pd3]])


# Just to align the Delta_V ylabel to the other 3 ylabel's
labelx = -0.075 # very close to the plot
axarr[0].yaxis.set_label_coords(labelx, 0.5, transform=None)


##### Y1 plot:
#f, axarr = plt.subplots(3, sharex=True)
axarr[1].set_ylabel('Y1', fontsize=15)

# Create a new axis:
axarr[1].grid()
ax2 = axarr[1].twiny()

# Make the ax1-ticks and ax1-tick-labels match the line color (blue):
axarr[1].tick_params('x', colors='blue')

# Make the ax2-ticks and ax2-tick-labels match the red color: 
ax2.tick_params('x', colors='red')
ax2.set_xticklabels([])  # disable the tic labels

# Set xlimits of ax2 the same as ax1
ax2.set_xlim(axarr[1].get_xlim())

# Set ticks at desired position
ind_pos_Bd3 = [0, 4, 8, 12, 16, 20, 24, 28, 32]
axarr[1].set_xticks(X1_orange[ind_pos_Bd3])
ax2.set_xticks(X1_orange[ind_pos_Bd3])

# Label ticks of ax2 with values from X2
#ax2.set_xticklabels(["%.2f" % i for i in P])
axarr[1].yaxis.set_major_formatter(mtick.FormatStrFormatter('%1.e'))

#### Y2 plot:
axarr[2].set_ylabel('Y2', fontsize=15)

# Create a new axis:
axarr[2].grid()
ax2 = axarr[2].twiny()

# Make the ax1-ticks and ax1-tick-labels match the line color (blue):
axarr[2].tick_params('x', colors='blue')

# Make the ax2-ticks and ax2-tick-labels match the red color: 
axarr[2].set_xlabel('X1', fontsize=14, color='blue')
# this also adds the numbers on top of the tics,
# but sets the colors of the tics
axarr[2].tick_params('x', colors='blue')

# Make the ax2-ticks and ax2-tick-labels match the red color: 
ax2.tick_params('x', colors='red')
ax2.set_xticklabels([])  # disable the tic labels

# Set xlimits of ax2 the same as ax1
ax2.set_xlim(axarr[2].get_xlim())

# Set ticks at desired position
ind_pos_Bd3 = [0, 4, 8, 12, 16, 20, 24, 28, 32]
axarr[2].set_xticks(X1_orange[ind_pos_Bd3])
ax2.set_xticks(X1_orange[ind_pos_Bd3])

# Label ticks of ax2 with values from X2
axarr[2].yaxis.set_major_formatter(mtick.FormatStrFormatter('%1.e'))


plt.show()

Answer 1

The trick is to add a new twin axis for each row of tick labels you want.

You can then position them properly setting the pad parameter in tick_params.

Allow me to make your example a little smaller so it's easier to follow

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker as mtick

fig, ax = plt.subplots(figsize=(12,2))

np.random.seed(42)
x0 = np.arange(50)
y0 = np.random.rand(50)
x1 = np.arange(30)
y1 = np.random.rand(30) + 0.7

ax.plot(x0, y0, ls='--', marker='o', ms=6, color='orange')
ax.grid(True)
ax.tick_params('x', colors='blue')
ax.set_xlabel('x1', fontsize=14, color='blue')
ax.set_ylabel('y', fontsize=14)

tax1 = ax.twiny()
tax1.set_xlim(ax.get_xlim())
tax1.tick_params('x', colors='orange', pad=14)
tax1.set_xlabel('x2', fontsize=14, color='red', labelpad=6)

tax2 = ax.twiny()
tax2.set_xlim(ax.get_xlim())
tax2.plot(x1, y1, ls='--', marker='o', ms=6, color='green')
tax2.tick_params('x', colors='green')
tax2.set_xticks([0, 10, 20, 30])

fig.savefig('img.png', pad_inches=0, bbox_inches='tight')

As you pointed out in the comments an issue with this plot is that you get green and orange tick lines and you would like to have them in red just like the x2 label.

You can hide the green tick lines setting length=0 in tick_params, draw the orange plot ticks in red first and then set labels color to orange.

Here's the modified code

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker as mtick

fig, ax = plt.subplots(figsize=(12,2))

np.random.seed(42)
x0 = np.arange(50)
y0 = np.random.rand(50)
x1 = np.arange(30)
y1 = np.random.rand(30) + 0.7

ax.plot(x0, y0, ls='--', marker='o', ms=6, color='orange')
ax.grid(True)
ax.tick_params('x', colors='blue')
ax.set_xlabel('x1', fontsize=14, color='blue')
ax.set_ylabel('y', fontsize=14)

tax1 = ax.twiny()
tax1.set_xlim(ax.get_xlim())
tax1.tick_params('x', colors='red', pad=14)
tax1.set_xlabel('x2', fontsize=14, color='red', labelpad=6)
[x.set_color("orange") for x in tax1.get_xticklabels()]

tax2 = ax.twiny()
tax2.set_xlim(ax.get_xlim())
tax2.plot(x1, y1, ls='--', marker='o', ms=6, color='green')
tax2.tick_params('x', colors='green', pad=6, length=0)
tax2.set_xticks([0, 10, 20, 30])

fig.savefig('img2.png', pad_inches=0, bbox_inches='tight')