Add date tickers to a matplotlib/python chart

Question

I have a question that sounds simple but it's driving me mad for some days. I have a historical time series closed in two lists: the first list is containing prices, let's say P = [1, 1.5, 1.3 ...] while the second list is containing the related dates, let's say D = [01/01/2010, 02/01/2010...]. What I would like to do is to plot SOME of these dates (when I say "some" is because the "best" result I got so far is to show all of them as tickers, so creating a black cloud of unreadable data in the x-axis) that, when you zoom in, are shown more in details. This picture is now having the progressive automated range made by Matplotlib:

Instead of 0, 200, 400 etc. I would like to have the dates values that are related to the data-point plotted. Moreover, when I zoom-in I get the following:

As well as I get the detail between 0 and 200 (20, 40 etc.) I would like to get the dates attached to the list. I'm sure this is a simple problem to solve but I'm new to Matplotlib as well as to Python and any hint would be appreciated. Thanks in advance

Answer 1

Matplotlib has sophisticated support for plotting dates. I'd recommend the use of AutoDateFormatter and AutoDateLocator. They are even locale-specific, so they choose month-names according to your locale.

import matplotlib.pyplot as plt
from matplotlib.dates import AutoDateFormatter, AutoDateLocator

xtick_locator = AutoDateLocator()
xtick_formatter = AutoDateFormatter(xtick_locator)

ax = plt.axes()
ax.xaxis.set_major_locator(xtick_locator)
ax.xaxis.set_major_formatter(xtick_formatter)

EDIT

For use with multiple subplots, use multiple locator/formatter pairs:

import datetime
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.dates import AutoDateFormatter, AutoDateLocator, date2num

x = [datetime.datetime.now() + datetime.timedelta(days=30*i) for i in range(20)]
y = np.random.random((20))

xtick_locator = AutoDateLocator()
xtick_formatter = AutoDateFormatter(xtick_locator)

for i in range(4):
    ax = plt.subplot(2,2,i+1)
    ax.xaxis.set_major_locator(xtick_locator)
    ax.xaxis.set_major_formatter(xtick_formatter)
    ax.plot(date2num(x),y)


plt.show()

Answer 2

You can do timeseries plot with pandas For detail refer this : http://pandas.pydata.org/pandas-docs/dev/timeseries.html and http://pandas.pydata.org/pandas-docs/dev/generated/pandas.Series.plot.html

import pandas as pd    
DateStrList = ['01/01/2010','02/01/2010']
P = [2,3]
D = pd.Series([pd.to_datetime(date) for date in DateStrList])
series =pd.Series(P, index=D)
pd.Series.plot(series)