pandas 如何在matplotlib中以'%H:%M'格式在y轴上绘制时间？
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how to plot time on y-axis in '%H:%M' format in matplotlib?
提问by themachinist
i would like to plot the times from a datetime64 series, where the y-axis is formatted as '%H:%M, showing only 00:00, 01:00, 02:00, etc.
我想绘制 datetime64 系列中的时间，其中 y 轴的格式为 '%H:%M，仅显示 00:00、01:00、02:00 等。
this is what the plot looks like without customizing the y-axis formatting.
这就是没有自定义 y 轴格式的绘图的样子。
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
from matplotlib.dates import DateFormatter
from matplotlib.dates import HourLocator
df = pd.DataFrame(data=dict(a=pd.date_range('1/1/2011',periods=1440000,freq='1min')))
df = df.iloc[np.arange(0,1440*100,1440)+np.random.randint(1,300,100)]
plt.plot(df.index,df['a'].dt.time)
plt.show()
After reading around on the topic on SO, I attempted the following but without success.
在阅读关于 SO 的主题后，我尝试了以下但没有成功。
ax = plt.subplot()
ax.yaxis.set_major_locator(HourLocator())
ax.yaxis.set_major_formatter(DateFormatter('%H:%M'))
plt.plot(df.index,df['a'].dt.time)
plt.show()
ValueError: DateFormatter found a value of x=0, which is an illegal date. This usually occurs because you have not informed the axis that it is plotting dates, e.g., with ax.xaxis_date()
Could anyone advise me?
有人可以建议我吗？
回答by Stop harming Monica
For that to work you need to pass datetimeobjects (and I mean datetime, not datetime64). You can convert all timestamps to the same date and then use .tolist()to get the actual datetimeobjects.
为此，您需要传递datetime对象（我的意思是datetime，不是datetime64）。您可以将所有时间戳转换为同一日期，然后用于.tolist()获取实际datetime对象。
y = df['a'].apply(lambda x: x.replace(year=1967, month=6, day=25)).tolist()
ax = plt.subplot()
ax.plot(df.index, y)
ax.yaxis.set_major_locator(HourLocator())
ax.yaxis.set_major_formatter(DateFormatter('%H:%M'))
回答by Hun
You can try two things: 1) It should be ax.xaxis.... not ax.yaxis.... 2) Use set_major_locator() instead of set_major_formatter() for Locator. Example is shown below.
您可以尝试两件事：1) 它应该是 ax.xaxis.... 而不是 ax.yaxis.... 2) 使用 set_major_locator() 而不是 set_major_formatter() 作为定位器。示例如下所示。
min = 15
ax.xaxis.set_major_locator(MinuteLocator(byminute=range(0,60,min)) )
ax.xaxis.set_major_formatter( DateFormatter('%H:%M') )
