python - Using datetime as ticks in Matplotlib

Question

I'm basically trying to plot a graph where the x axis represent the month of the year. The data is stored in a numpy.array, with dimensions k x months. Here it follows a minimal example (my data is not this crazy):

import numpy
import matplotlib
import matplotlib.pyplot as plt

cmap = plt.get_cmap('Set3')
colors = [cmap(i) for i in numpy.linspace(0, 1, len(complaints))]

data = numpy.random.rand(18,12)
y = range(data.shape[1])

plt.figure(figsize=(15, 7), dpi=200)
for i in range(data.shape[0]):
    plt.plot(y, data[i,:], color=colors[i], linewidth=5)
plt.legend(loc='center left', bbox_to_anchor=(1, 0.5)) 
plt.xticks(numpy.arange(0, 12, 1))
plt.xlabel('Hour of the Day')
plt.ylabel('Number of Complaints')
plt.title('Number of Complaints per Hour in 2015')

I'd like to have the xticks as strings instead of numbers. I'm wondering if I have to create a list of strings, manually, or if there is another way to translate the numbers to months. I have to do the same for weekdays, for example.

I've been looking to these examples:

http://matplotlib.org/examples/pylab_examples/finance_demo.html http://matplotlib.org/examples/pylab_examples/date_demo2.html

But I'm not using datetime.

Answer 1

This is an alternative plotting method plot_date, which you might want to use if your independent variable are datetime like, instead of using the more general plot method:

import datetime
data = np.random.rand(24)

#a list of time: 00:00:00 to 23:00:00
times = [datetime.datetime.strptime(str(i), '%H') for i in range(24)]

#'H' controls xticklabel format, 'H' means only the hours is shown
#day, year, week, month, etc are not shown
plt.plot_date(times, data, fmt='H')
plt.setp(plt.gca().xaxis.get_majorticklabels(),
         'rotation', 90)

The benefit of it is that now you can easily control the density of xticks, if we want to have a tick every hour, we will insert these lines after plot_date:

##import it if not already imported
#import matplotlib.dates as mdates
plt.gca().xaxis.set_major_locator(mdates.HourLocator())