python-matplotlib:x轴上的时间戳格式

我正在尝试在天气数据图中格式化x轴.我对y轴感到满意,但是到目前为止,我为使x轴成为一种体面的,人类可读的格式所做的所有尝试都没有奏效.因此,经过数小时的反复试验,希望能对您有所帮助.

ugly x-axis

我正在努力实现的目标

最后,我希望每30分钟就有一个刻度线,每小时有一个垂直的虚线网格线,其下方写有HH:MM的时间,另外还有每天晚上00:00点写的日期.诸如此类(注意,前面的ASCII艺术不好!):

     :         :         :
     :         :         :
     :         :         :
     :         :         :
     :         :         :
|====|====|====|====|====|====|====
   23:00     00:00     01:00
            09JAN18

所有时间都是UTC,这将是最终的豪华版本.但是我的问题是从更早开始的.

我的代码段

首先,我尝试将其转换为可读的格式.我想出了

locator = mdates.AutoDateLocator()
plt.gca().xaxis.set_major_locator(locator)
plt.gca().xaxis.set_major_formatter(mdates.AutoDateFormatter(locator))

希望我能摆脱经验

结果

输出不完全是我希望的:

[email protected]:~/wx-logging $python plot.py
[( 15.94,  57.86,  992.65,  1019.99, 1515460740)
 ( 15.96,  57.8 ,  992.65,  1019.99, 1515460745)
 ( 15.99,  57.79,  992.68,  1020.02, 1515460750) ...,
 ( 13.25,  55.7 ,  990.16,  1017.43, 1515496060)
 ( 13.31,  56.  ,  990.14,  1017.41, 1515496065)
 ( 13.34,  56.32,  990.13,  1017.4 , 1515496070)]
Traceback (most recent call last):
  File "plot.py", line 123, in 
    plt.savefig("plot.png", dpi=150)
  File "/usr/lib/python2.7/dist-packages/matplotlib/pyplot.py", line 697, in savefig
    res = fig.savefig(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/figure.py", line 1572, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/backend_bases.py", line 2244, in print_figure
    **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/backend_agg.py", line 545, in print_png
    FigureCanvasAgg.draw(self)
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/backend_agg.py", line 464, in draw
    self.figure.draw(self.renderer)
  File "/usr/lib/python2.7/dist-packages/matplotlib/artist.py", line 63, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/figure.py", line 1143, in draw
    renderer, self, dsu, self.suppressComposite)
  File "/usr/lib/python2.7/dist-packages/matplotlib/image.py", line 139, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/lib/python2.7/dist-packages/mpl_toolkits/axes_grid1/parasite_axes.py", line 295, in draw
    self._get_base_axes_attr("draw")(self, renderer)
  File "/usr/lib/python2.7/dist-packages/mpl_toolkits/axisartist/axislines.py", line 778, in draw
    super(Axes, self).draw(renderer, inframe)
  File "/usr/lib/python2.7/dist-packages/matplotlib/artist.py", line 63, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/axes/_base.py", line 2409, in draw
    mimage._draw_list_compositing_images(renderer, self, dsu)
  File "/usr/lib/python2.7/dist-packages/matplotlib/image.py", line 139, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/lib/python2.7/dist-packages/mpl_toolkits/axisartist/axis_artist.py", line 915, in draw
    gl = self._grid_helper.get_gridlines(self._which, self._axis)
  File "/usr/lib/python2.7/dist-packages/mpl_toolkits/axisartist/axislines.py", line 546, in get_gridlines
    locs.extend(self.axes.xaxis.major.locator())
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 983, in __call__
    self.refresh()
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 1003, in refresh
    dmin, dmax = self.viewlim_to_dt()
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 760, in viewlim_to_dt
    return num2date(vmin, self.tz), num2date(vmax, self.tz)
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 401, in num2date
    return _from_ordinalf(x, tz)
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 254, in _from_ordinalf
    dt = datetime.datetime.fromordinal(ix).replace(tzinfo=UTC)
ValueError: year is out of range
[email protected]:~/wx-logging $

并不完全有希望.我不知道为什么会说ValueError:year超出范围,因为它是unix时代的时间戳.

我究竟做错了什么?如何获得上面概述的预期结果?我非常感谢朝着正确方向前进.谢谢您的帮助!

祝一切顺利,
克里斯

完整的脚本

为了给您一些背景,到目前为止我完整的脚本.

#!/usr/bin/python
# -*- coding: utf-8 -*-

import matplotlib
matplotlib.use('AGG')
from mpl_toolkits.axes_grid1 import host_subplot
import mpl_toolkits.axisartist as aa
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
from matplotlib.ticker import FuncFormatter
import numpy as np
from numpy import vectorize
import datetime
import shutil
import math

# Dewpoint calculation
def dewpoint(tempC, rlHum):

    r  = 8314.3
    mw = 18.016

    if tempC >= 0:
        a = 7.5
        b = 237.3
    # over water:
    # elif tempC < 0:
    #     a = 7.6
    #     b = 240.7
    #
    # over ice:
    elif tempC < 0:
        a = 9.5
        b = 265.5

    saettDampfDruck = 6.1078 * 10**((a*tempC)/(b+tempC))
    dampfDruck = rlHum / 100.0 * saettDampfDruck
    v = math.log10(dampfDruck/6.1078)
    dewpC = b*v/(a-v)

    return dewpC

# translate cm into inches
def cm2inch(*tupl):
    inch = 2.54
    if isinstance(tupl[0], tuple):
        return tuple(i/inch for i in tupl[0])
    else:
        return tuple(i/inch for i in tupl)

vdewpoint = vectorize(dewpoint)

convertDate = lambda x: datetime.datetime.utcfromtimestamp(x)

data = np.genfromtxt('/home/pi/wx-logging/wx-log2.txt', 
                    delimiter=';', 
                    usecols=(1, 2, 3, 5, 6), 
                    names=['temp', 'humidity', 'press', 'slp', 'time'], 
                    converters={'6': convertDate}, 
                    dtype='float, float, float, float, int')

print data

plt.figure(figsize=cm2inch(29.7, 21))

host = host_subplot(111, axes_class=aa.Axes)
plt.subplots_adjust(right=0.75)
par1 = host.twinx()
par2 = host.twinx()

offset = 70 # offset of detached axis
new_fixed_axis = par2.get_grid_helper().new_fixed_axis
par2.axis["right"] = par2.get_grid_helper().new_fixed_axis(loc="right", 
                                                            axes=par2, 
                                                            offset=(offset, 0))

par1.axis["right"].toggle(all=True)
par2.axis["right"].toggle(all=True)

host.set_title("Weather Station")
host.set_xlabel("Time")
host.set_ylabel("Temperature & Dewpoint [" + u'\u00b0'+ "C]")
par1.set_ylabel("Sealevel Pressure [hPa]")
par2.set_ylabel("relative Humidity [%]")

host.set_ylim([-20, 40]) # temperature range -20C ... +40C
par1.set_ylim([980, 1040]) # slp range 980hPa ... 1040hPa
par2.set_ylim([0, 100]) # percent


p1, = host.plot(data['time'],
                data['temp'],
                label="Temperature",
                color="red",
                linewidth=2)
p2, = host.plot(data['time'],
                vdewpoint(data['temp'],
                data['humidity']),
                label="Dewpoint",
                color="salmon",
                linewidth=0.75)
p3, = par1.plot(data['time'],
                data['slp'],
                label="Sealevel Pressure",
                color="blue",
                linewidth=0.75)
p4, = par2.plot(data['time'],
                data['humidity'],
                label="rel. Humidity",
                color="grey",
                linewidth=0.5)

locator = mdates.AutoDateLocator()
plt.gca().xaxis.set_major_locator(locator)
plt.gca().xaxis.set_major_formatter(mdates.AutoDateFormatter(locator))


plt.legend(bbox_to_anchor=(0.05, 0.05), 
           loc=3,
           ncol=2, 
           borderaxespad=0.)

plt.savefig("plot.png", dpi=150)

shutil.copyfile('/home/pi/wx-logging/plot.png', '/var/www/html/plot.png')

EDIT1:您可以下载带有示例数据的wx-log2.txt(〜58KB),以试验脚本. tiago正确建议

最佳答案

您的代码有些错误.首先,在converters = {‘6’中使用引号中的列:意味着将永远不会应用转换功能.使用不带引号的列号:

converters={6: convertDate},

另一个问题是,您需要从字符串转换为整数,否则日期时间转换将不起作用:

convertDate = lambda x: datetime.datetime.utcfromtimestamp(int(x))

最后,您的时间字段的数据类型必须为numpy.datatype64(并以微秒为单位指定,因为utcfromtimestamp返回的内容).在np.genfromtxt调用中分配数据类型的正确方法如下:

data = np.genfromtxt('wx-log2.txt',  
                     delimiter=';',
                     converters={6: convertDate},
                     usecols=(1,2,3,5,6), 
                     dtype=[('temp', 'f'), ('humidity', 'f'), ('press', 'f'), 
                            ('slp', 'f'), ('time', 'datetime64[us]')])

通过上面的以下内容,您应该如何具有plt.plot_date可以理解的格式的时间.

对于日期格式,您可以通过将次要刻度标签设置为HH:MM并将主刻度号设置为一年中的日期来实现与您尝试实现的功能类似的功能,但是我不知道有什么其他方法每30分钟贴上未标记的刻度线.

这是一个简单的示例,具有正确的时间数组,并以与您所需格式相似的格式进行绘制.为简单起见,仅每4小时写一次刻度线,但您可以更改它.

import numpy as np
import matplotlib.dates as dates
import matplotlib.pyplot as plt 

fig, ax = plt.subplots()
idx = pd.date_range('2018-01-07', '2018-01-09', freq='10min')
# generate a time range series with 10 min intervals
idx = np.arange('2018-01-07T00', '2018-01-09T02', 10, dtype='datetime64[m]')
# some random data
y = np.sin(np.arange(idx.shape[0]) / 0.01)

ax.plot_date(idx, y, '-')

ax.xaxis.set_minor_locator(dates.HourLocator(interval=4))   # every 4 hours
ax.xaxis.set_minor_formatter(dates.DateFormatter('%H:%M'))  # hours and minutes
ax.xaxis.set_major_locator(dates.DayLocator(interval=1))    # every day
ax.xaxis.set_major_formatter(dates.DateFormatter('\n%d-%m-%Y')) 

output image