matplotlib: Creating two (stacked) subplots with SHARED X axis but SEPARATE Y axis values

Question

I am using matplotlib 1.2.x and Python 2.6.5 on Ubuntu 10.0.4. I am trying to create a SINGLE plot that consists of a top plot and a bottom plot.

The X axis is the date

Answer 1

There seem to be a couple of problems with your code:

1. If you were using figure.add_subplots with the full signature of subplot(nrows, ncols, plotNum) it may have been more apparent that your first plot asking for 1 row and 1 column and the second plot was asking for 2 rows and 1 column. Hence your first plot is filling the whole figure. Rather than fig.add_subplot(111) followed by fig.add_subplot(212) use fig.add_subplot(211) followed by fig.add_subplot(212).

2. Sharing an axis should be done in the add_subplot command using sharex=first_axis_instance

I have put together an example which you should be able to run:

import matplotlib.pyplot as plt
import matplotlib.ticker as mticker
import matplotlib.dates as mdates


import datetime as dt


n_pts = 10
dates = [dt.datetime.now() + dt.timedelta(days=i) for i in range(n_pts)]

ax1 = plt.subplot(2, 1, 1)
ax1.plot(dates, range(10))

ax2 = plt.subplot(2, 1, 2, sharex=ax1)
ax2.bar(dates, range(10, 20))

# Now format the x axis. This *MUST* be done after all sharex commands are run.

# put no more than 10 ticks on the date axis.  
ax1.xaxis.set_major_locator(mticker.MaxNLocator(10))
# format the date in our own way.
ax1.xaxis.set_major_formatter(mdates.DateFormatter('%Y-%m-%d'))

# rotate the labels on both date axes
for label in ax1.xaxis.get_ticklabels():
    label.set_rotation(30)
for label in ax2.xaxis.get_ticklabels():
    label.set_rotation(30)

# tweak the subplot spacing to fit the rotated labels correctly
plt.subplots_adjust(hspace=0.35, bottom=0.125)

plt.show()

Hope that helps.