Matplotlib pyplot - tick control and showing date

Question

My matplotlib pyplot has too many xticks - it is currently showing each year and month for a 15-year period, e.g. "2001-01", but I only want the x-axis to show the year (e.g. 2001).

The output will be a line graph where x-axis shows dates and the y-axis shows the sale and rent prices.

# Defining the variables
ts1 = prices['Month'] # eg. "2001-01" and so on
ts2 = prices['Sale'] 
ts3 = prices['Rent'] 

# Reading '2001-01' as year and month
ts1 = [dt.datetime.strptime(d,'%Y-%m').date() for d in ts1]

plt.figure(figsize=(13, 9))
# Below is where it goes wrong. I don't know how to set xticks to show each year. 
plt.xticks(ts1, rotation='vertical')
plt.xlabel('Year')
plt.ylabel('Price')
plt.plot(ts1, ts2, 'r-', ts1, ts3, 'b.-')
plt.gcf().autofmt_xdate()
plt.show()

Answer 1

Try removing the plt.xticks function call altogether. matplotlib will then use the default AutoDateLocator function to find the optimum tick locations.

Alternatively if the default includes some months which you don't want then you can use matplotlib.dates.YearLocator which will force the ticks to be years only.

You can set the locator as shown below in a quick example:

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

x = [dt.datetime.utcnow() + dt.timedelta(days=i) for i in range(1000)]
y = range(len(x))

plt.plot(x, y)

locator = mdate.YearLocator()
plt.gca().xaxis.set_major_locator(locator)

plt.gcf().autofmt_xdate()

plt.show()

Answer 2

You can do this with plt.xticks.

As an example, here I have set the xticks frequency to display every three indices. In your case, you would probably want to do so every twelve indices.

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(10)
y = np.random.randn(10)

plt.plot(x,y)
plt.xticks(np.arange(min(x), max(x)+1, 3))
plt.show()

In your case, since you are using dates, you can replace the argument of the second to last line above with something like ts1[0::12], which will select every 12th element from ts1 or np.arange(0, len(dates), 12) which will select every 12th index corresponding to the ticks you want to show.