python - Plot date and time (x axis) versus a value (y axis) using data from file

Question

I have data in a file (.dat) in the format of

%dd %mm %yyyy %HH %MM %SS value

separated by spaces. I would like to plot the day, month, year and time on the x-axis, and the value on the y-axis. It should always be reading it from the file, as I have many files that are very large to analyze.

My latest attempt:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
from time import gmtime, strftime
date, time, level = np.loadtxt('my_file.txt', unpack=True, usecols = (0,1,2,3), converters={ 0,1: mdates.strpdate2num('%dd/%mm/%YY %HH:%MM')}) #read format of file
# then to plot 
plt.plot_date(x=date, y=level, fmt='%dd/%mm/%YY %HH:%MM') # fmt is changed from r- 
plt.title('title')
plt.ylabel('Waterlevel (m)')
plt.grid(True)
plt.show()

Answer 1

If I have understood your problem correctly, I believe this is a possible solution:

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

# Converter function
datefunc = lambda x: mdates.date2num(datetime.strptime(x, '%d %m %Y %H %M %S'))

# Read data from 'file.dat'
dates, levels = np.genfromtxt('file.dat',    # Data to be read
                              delimiter=19,  # First column is 19 characters wide
                              converters={0: datefunc}, # Formatting of column 0
                              dtype=float,   # All values are floats
                              unpack=True)   # Unpack to several variables

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

# Configure x-ticks
ax.set_xticks(dates) # Tickmark + label at every plotted point
ax.xaxis.set_major_formatter(mdates.DateFormatter('%d/%m/%Y %H:%M'))

ax.plot_date(dates, levels, ls='-', marker='o')
ax.set_title('title')
ax.set_ylabel('Waterlevel (m)')
ax.grid(True)

# Format the x-axis for dates (label formatting, rotation)
fig.autofmt_xdate(rotation=45)
fig.tight_layout()

fig.show()

With file.dat being e.g.

01 06 2013 00 00 00 24.23
02 06 2013 01 00 00 22.23
03 06 2013 02 00 00 21.43
04 06 2013 03 00 00 24.32
04 06 2013 14 30 00 23.42
06 06 2013 03 00 00 24.32
07 06 2013 19 20 00 23.54
08 06 2013 03 00 00 26.23
08 06 2013 19 00 00 24.43
10 06 2013 12 40 00 23.22

the output becomes like this: