matplotlib: Plot graph using time and ignoring year/month/date

Question

I am a novice to Python/matplotlib so please bear with me! I have a list of epoch timestamps across several days and a boolean indicating whether an event occurred or not. I want to plot this using matplotlib with time on x-axis and Y-axis showing 1/0 and I see SO examples Plotting time in Python with Matplotlib for doing this.

However, I want to ignore the yr/month/date and plot only again time, i.e. 8 AM time on 1-Dec and 8 AM time on 2-Dec use the same X-axis coordinate.

Edit: Here is the current code:

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

event = [
(1384528771000000000, 1),
(1384550132000000000, 0),
(1384881104000000000, 0),
(1384962750000000000, 1),
(1384966615000000000, 1),
(1385049149000000000, 1),
(1385053051000000000, 0),
(1385053939000000000, 0),
(1385140573000000000, 1),
(1385393839000000000, 1),
(1385398965000000000, 0),
(1385410739000000000, 1),
(1385483309000000000, 1),
(1385587272000000000, 0),
(1385998456000000000, 1),
(1386084047000000000, 0),
(1386085865000000000, 1),
(1386259016000000000, 0),
(1386345606000000000, 0),
(1386602368000000000, 1)
]

for line in event:
    timeStmp = datetime.datetime.strptime(time.ctime(line[0]/1000000000), "%a %b %d %H:%M:%S %Y")
    print timeStmp, mdates.date2num(timeStmp)
    plt.plot_date(mdates.date2num(timeStmp),line[1])
plt.show()

@inquisitiveIdiot note this is a matplotlib/python, not MATLAB question. — tacaswell
– tacaswell, Commented Dec 16, 2013 at 18:28
What have you tried? You will get much better help fixing broken code than asking us to write your code for you. You just need to convert your time stamps to datetime objects, then drop the date part. You should be able to directly plot the time vs your y values. — tacaswell
– tacaswell, Commented Dec 16, 2013 at 18:30

Paul H · Accepted Answer · 2013-12-16 23:21:32Z

1

So the only thing I'm doing differently here, is taking your date/time stamps, converting to a string of just time data, then using mdates to convert that time string to a number. Crude and inefficient, but I think it's what you want.

for line in event:
    datetimeStamp = datetime.datetime.strptime(time.ctime(line[0]/1000000000), "%a %b %d %H:%M:%S %Y")
    timeStamp = datetimeStamp.strftime('%H:%M:%S')

    print(timeStamp, mdates.datestr2num(timeStamp))
    plt.plot_date(mdates.datestr2num(timeStamp),line[1])
plt.show()

answered Dec 16, 2013 at 23:21

Paul H

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Troy Rockwood · Accepted Answer · 2013-12-16 23:49:59Z

Here is one way to do this, just plot the time difference between the beginning of the day and the time in the timestamp:

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

event = [
(1384528771000000000, 1),
(1384550132000000000, 0),
(1384881104000000000, 0),
(1384962750000000000, 1),
(1384966615000000000, 1),
(1385049149000000000, 1),
(1385053051000000000, 0),
(1385053939000000000, 0),
(1385140573000000000, 1),
(1385393839000000000, 1),
(1385398965000000000, 0),
(1385410739000000000, 1),
(1385483309000000000, 1),
(1385587272000000000, 0),
(1385998456000000000, 1),
(1386084047000000000, 0),
(1386085865000000000, 1),
(1386259016000000000, 0),
(1386345606000000000, 0),
(1386602368000000000, 1)
]

fig = plt.figure()
ax = fig.add_subplot(111)

for line in event:
    timeStmp = datetime.datetime.strptime(time.ctime(line[0]/1000000000), "%a %b %d %H:%M:%S %Y")
    print timeStmp, mdates.date2num(timeStmp)
    tdelta = timeStmp - datetime.datetime.strptime(str(timeStmp.year) + " " + str(timeStmp.month) + " " + str(timeStmp.day) + " 00:00:00", "%Y %m %d %H:%M:%S")
    ax.plot(tdelta.total_seconds(),line[1], 'o')

def timeTicks(x, pos):
    d = datetime.timedelta(seconds=x)
    return str(d)
formatter = matplotlib.ticker.FuncFormatter(timeTicks)
ax.xaxis.set_major_formatter(formatter)
plt.show()

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