Matplotlib: Formatting date in day.month.year style

Question

I want to plot some lines with the date on the x axis, but all examples I could find use the American style like 12-31-2012. But I want 31.12.2012, but it doesn't seem to work by just changing the date formatter from

dateFormatter = dates.DateFormatter('%Y-%m-%d')

to

dateFormatter = dates.DateFormatter('%d.%m.%y')

My date list works like this: I want to define a "firstDay" manually, and then generate X succeeding days. That works as I can see when I print that result list. But when I want to plot that list (converted by num2date) I have totally different dates.

E.g. I set my firstDay to 734517.0 which is January the 15th in 2012. Then I print my dates on the axis and I get as a first date 01.01.87 ??

Here is my full code:

import numpy as np
import matplotlib.pyplot as plot
import matplotlib.ticker as mticker
from matplotlib import dates
import datetime

fig = plot.figure(1)
DAU = (  2,  20,  25,  60, 190, 210,  18, 196, 212, 200, 160, 150, 185, 175, 316, 320, 294, 260, 180, 145, 135,  97,  84,  80,  60,  45,  37,  20,  20,  24,  39,  73,  99)
WAU = ( 50, 160, 412, 403, 308, 379, 345, 299, 258, 367, 319, 381, 461, 412, 470, 470, 468, 380, 290, 268, 300, 312, 360, 350, 316, 307, 289, 321, 360, 378, 344, 340, 346)
MAU = (760, 620, 487, 751, 612, 601, 546, 409, 457, 518, 534, 576, 599, 637, 670, 686, 574, 568, 816, 578, 615, 520, 499, 503, 529, 571, 461, 614, 685, 702, 687, 649, 489)

firstDay = 734517.0     #15. Januar 2012

#create an array with len(DAU) entries from given starting day...
dayArray = []
for i in xrange(len(DAU)):
    dayArray.append(firstDay + i)

#...and fill them with the converted dates
dayLabels = [dates.num2date(dayArray[j]) for j in xrange(len(DAU))]

for k in xrange(len(DAU)):
    print dayLabels[k]

spacing = np.arange(len(DAU)) + 1

line1 = plot.plot(spacing, DAU, 'o-', color = '#336699')
line2 = plot.plot(spacing, WAU, 'o-', color = '#993333')
line3 = plot.plot(spacing, MAU, 'o-', color = '#89a54e')

ax = plot.subplot(111)
plot.ylabel('', weight = 'bold')
plot.title('', weight = 'bold')
ticks, labels = plot.xticks(spacing, dayLabels)
plot.setp(labels, rotation = 90, fontsize = 11)

dateFormatter = dates.DateFormatter('%d.%m.%y')
ax.xaxis.set_major_formatter(dateFormatter)
#ax.fmt_xdata = dates.DateFormatter('%Y-%m-%d')
#fig.autofmt_xdate()

yMax = max(np.max(DAU), np.max(WAU), np.max(MAU))
yLimit = 100 - (yMax % 100) + yMax
plot.yticks(np.arange(0, yLimit + 1, 100))

plot.grid(True, axis = 'y')
plot.subplots_adjust(bottom = 0.5)
plot.subplots_adjust(right = 0.82)

legend = plot.legend((line1[0], line2[0], line3[0]),
                     ('DAU',
                     'WAU',
                     'MAU'),
                     'upper left',
                     bbox_to_anchor = [1, 1],
                     shadow = True)

frame = legend.get_frame()
frame.set_facecolor('0.80')
for t in legend.get_texts():
    t.set_fontsize('small')

plot.show()

It would be fine as well with this date formatter:

ax.fmt_xdata = dates.DateFormatter('%Y-%m-%d')

but that gives me the timestamps as well, e.g. 2012-01-15 00:00:00+00:00 . If someone could tell me how to cut the time off, it would be really great!!

Answer 1

It seems to me that the easiest way is to use real Datetime objects. This way you can use the datetime.timedelta(days=i) to make your date range. And matplotlib automatically takes spacing into account in case your dates are not regular. It also allows you to use the default date formatting options from matplotlib.

I left some code out to keep it simpler but you should be able to mix this with your script:

![import numpy as np
import matplotlib.pyplot as plot
import matplotlib.ticker as mticker
from matplotlib import dates
import datetime

fig = plot.figure(1)
DAU = (  2,  20,  25,  60, 190, 210,  18, 196, 212, 200, 160, 150, 185, 175, 316, 320, 294, 260, 180, 145, 135,  97,  84,  80,  60,  45,  37,  20,  20,  24,  39,  73,  99)
WAU = ( 50, 160, 412, 403, 308, 379, 345, 299, 258, 367, 319, 381, 461, 412, 470, 470, 468, 380, 290, 268, 300, 312, 360, 350, 316, 307, 289, 321, 360, 378, 344, 340, 346)
MAU = (760, 620, 487, 751, 612, 601, 546, 409, 457, 518, 534, 576, 599, 637, 670, 686, 574, 568, 816, 578, 615, 520, 499, 503, 529, 571, 461, 614, 685, 702, 687, 649, 489)

firstDay = datetime.datetime(2012,1,15)     #15. Januar 2012
   
dayArray = [firstDay + datetime.timedelta(days=i) for i in xrange(len(DAU))]

ax = plot.subplot(111)

line1 = ax.plot(dayArray, DAU, 'o-', color = '#336699')
line2 = ax.plot(dayArray, WAU, 'o-', color = '#993333')
line3 = ax.plot(dayArray, MAU, 'o-', color = '#89a54e')

ax.xaxis.set_major_formatter(dates.DateFormatter('%d.%m.%Y'))]

The main difference with your script is the way dayArray is created (and used as the x-value in the plotting command) and the last line which sets the format of the x-axis.