Plotting dates on the x-axis

Question

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?

help(num2date): "x is a float value which gives one plus the number of days since 0001-01-01", so x=19910102 does not correspond to 02 Jan 1991 — Kyss Tao, Mar 09 '12 at 01:51

mechanical_meat · Answer 1 · 2012-03-09T03:49:54.357

187

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:

enter image description here

edited Mar 09 '12 at 03:49

answered Mar 09 '12 at 02:02

mechanical_meat

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@bernie Thanks, it really helped me. However, in my problem I have too many days, so the whole plot gets clogged up. How to show every fifth date, or every tenth date on the x-axis with your method? – user1506145 Jul 03 '13 at 08:26
2

@erik I know this is a bit late, but I removed the two set_major lines and that cleared it up for me. Lost some functionality, but still an improvement. – TheBoro Mar 18 '16 at 09:19
1

Unfortunately, it shows me not 3 dates, but 6 other dates (in that interval though). Using matplotlib-1.5.1 – Groosha May 22 '16 at 09:16
Your example (from 2012) does not work for me (in 2023): I get `TypeError: float() argument must be a string or a number, not 'datetime.date'` for `plt.plot(x, y)`. Using “Python 3.9.2 (default, Feb 28 2021, 17:03:44) [GCC 10.2.1 20210110] on linux”, matplotlib 3.7.1. – PointedEars Mar 20 '23 at 18:44

Jacek Szałęga · Answer 2 · 2022-08-08T16:15:19.683

78

I have too low reputation to add comment to @bernie response, with response to @user1506145. I have run in to same issue.

The answer to it is an interval parameter which fixes things up

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import numpy as np
import datetime as dt

np.random.seed(1)

N = 100
y = np.random.rand(N)

now = dt.datetime.now()
then = now + dt.timedelta(days=100)
days = mdates.drange(now,then,dt.timedelta(days=1))

plt.gca().xaxis.set_major_formatter(mdates.DateFormatter('%Y-%m-%d'))
plt.gca().xaxis.set_major_locator(mdates.DayLocator(interval=5))
plt.plot(days,y)
plt.gcf().autofmt_xdate()
plt.show()

edited Aug 08 '22 at 16:15

answered Oct 24 '19 at 15:34

Jacek Szałęga

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Please note that if you are taking the first date of a series or index and the last date, then since this is a range the last date will be cutoff, and you will run into errors with your code. Assuming you have a `Date` column on your index, then you can do: `days = mdates.drange(d1.index.min(),d1.index.max() + dt.timedelta(days=1),dt.timedelta(days=1))`. Essentially, I added 1 day to the the date of the upperbound value of the range. – David Erickson Dec 05 '20 at 04:16
What changes should I do in Jacek Szałęga's code in order, not to assign random dates on x-axis, but put on x-axis dates gathered/sampled from excel file? – just_learning Sep 10 '21 at 07:16
2

Better to use `mdates.AutoDateLocator()` instead of `mdates.DayLocator(interval=5)` here to automatically calculate how many date labels should be shown on the x-axis. This may answer @just_learning 's question above. – HongchaoZhang Sep 15 '22 at 03:11

score 26 · Accepted Answer · answered Mar 09 '12 at 01:58

26

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'

answered Mar 09 '12 at 01:58

mathematical.coffee

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It would be nice if you could add the `import` statement as well, to help python novices like me. – kkuilla Mar 06 '20 at 10:13
@kkuilla If this is still relevant, I'm guessing he has it as `import matplotlib.dates as dates` – Ira I.I. Feb 25 '21 at 20:11
@IraI.I. You meant `from matplotlib import dates`? – Shayan Jul 26 '22 at 06:01

score 2 · Answer 4 · answered Apr 04 '22 at 15:25

Adapting @Jacek Szałęga's answer for the use of a figure fig and corresponding axes object ax:

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import numpy as np
import datetime as dt

np.random.seed(1)

N = 100
y = np.random.rand(N)

now = dt.datetime.now()
then = now + dt.timedelta(days=100)
days = mdates.drange(now,then,dt.timedelta(days=1))


fig = plt.figure()
ax = fig.add_subplot(111)
    
ax.plot(days,y)
ax.xaxis.set_major_formatter(mdates.DateFormatter('%Y-%m-%d'))
ax.xaxis.set_major_locator(mdates.DayLocator(interval=5))
ax.tick_params(axis='x', labelrotation=45)

plt.show()

score 1 · Answer 5 · answered Mar 27 '23 at 13:14

date = raw_date[:20]
# plot lines
plt.plot(date,target[:20] , label = "Real")
plt.xlabel('Date', fontsize=10)
plt.ylabel('Ylabel', fontsize=10)
plt.legend()
plt.title('Date to show')
plt.xticks(date_to_show_as_list,rotation=90)
plt.figure().set_figwidth(30)
plt.show()

Plotting dates on the x-axis

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