为什么在尝试使用 matplotlib 绘制它们时时间是 00:00？

Question

我有一个列表datetime，我正在尝试绘制一个数字，其中时间在 y 轴上，日期在 x 轴上。以下是我到目前为止所得到的：

import datetime as dt

import matplotlib.pyplot as plt

from matplotlib.dates import DateFormatter

datetimes_str = ['2020-08-03T03:46:18.000Z', '2020-08-01T01:14:31.000Z',

                 '2020-07-27T22:45:11.000Z', '2020-07-21T20:00:42.000Z',

                 '2020-07-20T00:37:17.000Z', '2020-07-16T00:40:47.000Z']

datetimes = [dt.datetime.strptime(d, "%Y-%m-%dT%H:%M:%S.%fZ") for d in datetimes_str]

# The above list contains datetimes:

# 2020-08-03 03:46:18

# 2020-08-01 01:14:31

# 2020-07-27 22:45:11

# 2020-07-21 20:00:42

# 2020-07-20 00:37:17

# 2020-07-16 00:40:47

fig, ax = plt.subplots()

ax.plot(datetimes, datetimes)

ax.yaxis.set_major_formatter(DateFormatter('%H:%M'))

ax.xaxis.set_major_formatter(DateFormatter('%Y/%m/%d'))

fig.autofmt_xdate()

plt.show()

上面的代码导致 -

如您所见，日期是正确的，但所有时间都是00:00。有什么问题？！

还有一些奇怪的事情：在列表中datetimes，当所有日期都相同且时间不同时，一切正常！

Answer 1

这是因为DateFormatter从日期的序数值中删除了浮点数：~/.local/bin/anaconda3/lib/python3.7/site-packages/matplotlib/dates.py in _from_ordinalf(x, tz)&nbsp; &nbsp; 281&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;tz = _get_rc_timezone()&nbsp; &nbsp; 282&nbsp;--> 283&nbsp; &nbsp; &nbsp;ix, remainder = divmod(x, 1)&nbsp; &nbsp; 284&nbsp; &nbsp; &nbsp;ix = int(ix)&nbsp; &nbsp; 285&nbsp; &nbsp; &nbsp;if ix < 1:您必须使用ax.set_yticks或最好创建自己的刻度/刻度标签ax.set_yticklabels

Answer 2

您可以在列表理解中对时间进行切片：import datetime as dtimport matplotlib.pyplot as pltfrom matplotlib.dates import DateFormatterdatetimes_str = ['2020-08-03T03:46:18.000Z', '2020-08-01T01:14:31.000Z',&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;'2020-07-27T22:45:11.000Z', '2020-07-21T20:00:42.000Z',&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;'2020-07-20T00:37:17.000Z', '2020-07-16T00:40:47.000Z']datetimes = [dt.datetime.strptime(d, "%Y-%m-%dT%H:%M:%S.%fZ") for d in datetimes_str]times = sorted([d[11:16] for d in datetimes_str])fig, ax = plt.subplots()ax.plot(datetimes, times)ax.xaxis.set_major_formatter(DateFormatter('%Y/%m/%d'))fig.autofmt_xdate()plt.show()制作：

Answer 3

发生这种情况是因为 x 轴和 y 轴唯一不同的是表示日期时间的格式，而不是日期时间本身的值，这就是为什么你总是会得到一条对角线。所以只显示 00:00，因为 y 轴的值变化太大而无法精确表示小时数。为了更改此设置，您需要通过删除日期信息并仅保留时间来更改 y 轴的值。这是一个应该可以解决问题的代码片段：import datetime as dtimport matplotlib.pyplot as pltfrom matplotlib.dates import DateFormatter, DayLocator, HourLocatordatetimes_str = ['2020-08-03T03:46:18.000Z', '2020-08-01T01:14:31.000Z',&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;'2020-07-27T22:45:11.000Z', '2020-07-21T20:00:42.000Z',&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;'2020-07-20T00:37:17.000Z', '2020-07-16T00:40:47.000Z']datetimes = [dt.datetime.strptime(d, "%Y-%m-%dT%H:%M:%S.%fZ") for d in datetimes_str]times = [d.replace(day=1, month=1, year=2000) for d in datetimes]# The above list contains datetimes:# 2020-08-03 03:46:18# 2020-08-01 01:14:31# 2020-07-27 22:45:11# 2020-07-21 20:00:42# 2020-07-20 00:37:17# 2020-07-16 00:40:47fig, ax = plt.subplots()ax.yaxis.set_major_formatter(DateFormatter('%H:%M'))ax.xaxis.set_major_formatter(DateFormatter('%Y/%m/%d'))ax.plot(datetimes, times)fig.autofmt_xdate()plt.show()