Plotting dates on the x-axis with Python's mat

问题:

I am trying to plot information against dates. I have a list of dates in the format \"01/02/1991\".

I converted them by doing the following:

x = parser.parse(date).strftime(\'%Y%m%d\'))

which gives 19910102

Then I tried to use num2date

import matplotlib.dates as dates
new_x = dates.num2date(x)

Plotting:

plt.plot_date(new_x, other_data, fmt=\"bo\", tz=None, xdate=True)

But I get an error. It says \"ValueError: year is out of range\". Any solutions?

回答1:

As @KyssTao has been saying, help(dates.num2date) says that the x has to be a float giving the number of days since 0001-01-01 plus one. Hence, 19910102 is not 2/Jan/1991, because if you counted 19910101 days from 0001-01-01 you\'d get something in the year 54513 or similar (divide by 365.25, number of days in a year).

Use datestr2num instead (see help(dates.datestr2num)):

new_x = dates.datestr2num(date) # where date is \'01/02/1991\'

回答2:

You can do this more simply using plot() instead of plot_date().

First, convert your strings to instances of Python datetime.date:

import datetime as dt

dates = [\'01/02/1991\',\'01/03/1991\',\'01/04/1991\']
x = [dt.datetime.strptime(d,\'%m/%d/%Y\').date() for d in dates]
y = range(len(x)) # many thanks to Kyss Tao for setting me straight here

Then plot:

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

plt.gca().xaxis.set_major_formatter(mdates.DateFormatter(\'%m/%d/%Y\'))
plt.gca().xaxis.set_major_locator(mdates.DayLocator())
plt.plot(x,y)
plt.gcf().autofmt_xdate()

Result: