On Thu, Jun 17, 2010 at 11:39 AM, Bill Eaton <e...@aeroantenna.com> wrote:
> I'm struggling to figure out how to format my data so that I can use dates
> as x-data.
<SNIP>
> I tried to import my own data. It looks like
> 2005-03-04,0.923115796
> 2005-03-05,0.915828724
> 2005-03-06,0.442521474
> 2005-03-07,0.997096213
> 2005-03-08,0.867752118
> And to import, I use recarray
> myarray = np.loadtxt(fullfile, dtype=[('date', '|O4'), ('ydata',
> 'float')], delimiter = ',')
> rx = myarray.view(np.recarray)
>
> Data imports fine. But when I go to plot, I get the following error
> ValueError: setting an array element with a sequence.
> WARNING: Failure executing file: <bogus.py>
You need to give np.loadtxt a converter so that it converts that first
column of strings into datetime objects:
import numpy as np
import matplotlib.pyplot as plt
from matplotlib import dates
from datetime import datetime
from StringIO import StringIO
s='''
2005-03-04,0.923115796
2005-03-05,0.915828724
2005-03-06,0.442521474
2005-03-07,0.997096213
2005-03-08,0.867752118'''
dateparser = lambda s: datetime.strptime(s, '%Y-%m-%d')
dt = np.dtype([('date', np.object),('ydata', np.float)])
d = np.loadtxt(StringIO(s), dtype=dt, converters={0:dateparser}, delimiter=',')
plt.plot(d['date'], d['ydata'])
plt.gca().xaxis.set_major_locator(dates.DayLocator())
plt.gca().xaxis.set_major_formatter(dates.DateFormatter('%Y/%m/%d'))
plt.show()
Personally, I find it much easier to work with python datetime objects
than any other form. You can
Ryan
--
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma
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