CODEWITHSUNDEEP
matplotlib
Artium
Artium

Reputation: 5331

Forcing ticks to appear at specific dates when using plot_date

This code will produce the figure below:

import math
import matplotlib.pyplot as plt
from matplotlib.dates import (YEARLY,HOURLY, DateFormatter,
                              drange)
import datetime


date1 = datetime.datetime(1952, 1, 1, 1, 1, 1)
date2 = datetime.datetime(1952, 1, 1, 23, 59, 59)
delta = datetime.timedelta(minutes= 10)

dates = drange(date1, date2, delta)
y = [math.sin(x/10.0) for x,_ in enumerate(dates)]

fig, ax = plt.subplots()

plt.plot_date(dates, y)

plt.plot_date([dates[15],dates[121]], [y[15], y[121]], marker="*", c="yellow", markersize=20)

ax.xaxis.set_major_formatter(DateFormatter('%H:%M:%S'))
ax.xaxis.set_tick_params(rotation=45, labelsize=10)

fig.autofmt_xdate()

plt.show()

enter image description here

I wish to indicate when the two events marked by a star happened.

How do force pyplot to draw a tick under the locations of the two stars?

I figured out that I need to use custom locator. But how exactly? It looks like it will produce evenly spaced ruler only.

rule = rrulewrapper(???)  
loc = RRuleLocator(rule)

Upvotes: 0

Views: 132

Answers (1)

ImportanceOfBeingErnest
ImportanceOfBeingErnest

Reputation: 339775

If you have a defined location of the ticks, you can use the FixedLocator.

import math
import matplotlib.pyplot as plt
from matplotlib.dates import DateFormatter, drange
from matplotlib.ticker import FixedLocator
import datetime


date1 = datetime.datetime(1952, 1, 1, 1, 1, 1)
date2 = datetime.datetime(1952, 1, 1, 23, 59, 59)
delta = datetime.timedelta(minutes= 10)

dates = drange(date1, date2, delta)
y = [math.sin(x/10.0) for x,_ in enumerate(dates)]

fig, ax = plt.subplots()

plt.plot_date(dates, y)

events, = plt.plot_date([dates[15],dates[121]], [y[15], y[121]], 
                   marker="*", c="r", markersize=20, ls="")

ax.xaxis.set_major_formatter(DateFormatter('%H:%M:%S'))
ax.xaxis.set_tick_params(which="major", rotation=30, labelsize=9)

ax.xaxis.set_minor_locator(FixedLocator(events.get_xdata()))
ax.xaxis.set_minor_formatter(DateFormatter('%H:%M:%S'))
ax.xaxis.set_tick_params(which="minor", rotation=30, labelsize=10, labelcolor="r")

plt.setp(ax.get_xticklabels(which="both"), ha="right")
plt.show()

enter image description here

I made the special ticklabels red, because they overlap the existing ticklabels. I guess you need to decide for yourself how you want to have it appear in the end.

Upvotes: 1

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