matplotlib的一个顺序问题

测试matplotlib的横纵坐标时间日期格式定义

遇到好奇怪的问题，一定要这个顺序

import matplotlib
matplotlib.use('Agg')

from matplotlib.pyplot import plot,savefig
import pylab as pl

否则运行时是提示如下

 File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1767, in __init__
    self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
_tkinter.TclError: no display name and no $DISPLAY environment variable

关于时间x轴的定义demo如下:

参考http://www.zeuux.com/group/scipython/bbs/content/51470/

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用loadtxt载入数据时，用object作为元素类型。

然后将日期和时间相加，并转换成列表，然后调用pl.datestr2num将日期字符串转换成一个数值。

绘图时调用plot_date()。对于日期和时间的格式化，请参考matplotlib网站的演示程序。

# -*- coding: utf-8 -*-




import numpy as np

import pylab as pl




t = np.loadtxt("data.txt", np.object)

date = pl.datestr2num( list(t[:,0] + " " + t[:,1]) )

value = t[:,2].astype(np.float)




pl.plot_date(date, value)

pl.show()

------------------------------------------------------------------------------------

[popexizhi]

关于np.loadtxt加载速度问题，参考http://stackoverflow.com/questions/14985233/load-text-file-as-strings-using-numpy-loadtxt

Is it essential that you need a numpy array? Otherwise you could speed things up by loading the data as a nested list.
def load(fname):
    ''' load the file using std open'''
    f = open(fname,'r')

    data = []
    for line in f.readlines():
        data.append(line.replace('\n','').split(' '))

    f.close()

    return data

For a textfile with 4000x4000 words this is about 10 times faster than loadtxt.

[popexizhi ]没有自己测试但是感觉大数据这个会有问题，[next]测试一下，有结果的blog一下