How to plot data against specific dates on the x-axis using matplotlib

Question

I have a dataset consisting of date-value pairs. I want to plot them in a bar graph with the specific dates in the x-axis.

My problem is that matplotlib

Answer 1

What you're doing is simple enough that it's easiest to just using plot, rather than plot_date. plot_date is great for more complex cases, but setting up what you need can be easily accomplished without it.

e.g., Based on your example above:

import datetime as DT
from matplotlib import pyplot as plt
from matplotlib.dates import date2num

data = [(DT.datetime.strptime('2010-02-05', "%Y-%m-%d"), 123),
        (DT.datetime.strptime('2010-02-19', "%Y-%m-%d"), 678),
        (DT.datetime.strptime('2010-03-05', "%Y-%m-%d"), 987),
        (DT.datetime.strptime('2010-03-19', "%Y-%m-%d"), 345)]

x = [date2num(date) for (date, value) in data]
y = [value for (date, value) in data]

fig = plt.figure()

graph = fig.add_subplot(111)

# Plot the data as a red line with round markers
graph.plot(x,y,'r-o')

# Set the xtick locations to correspond to just the dates you entered.
graph.set_xticks(x)

# Set the xtick labels to correspond to just the dates you entered.
graph.set_xticklabels(
        [date.strftime("%Y-%m-%d") for (date, value) in data]
        )

plt.show()

If you'd prefer a bar plot, just use plt.bar(). To understand how to set the line and marker styles, see plt.plot() Plot with date labels at marker locations http://www.geology.wisc.edu/~jkington/matplotlib_date_labels.png