[英]Add trend line to datetime matplotlib line graph
I have a pandas dataframe df:我有一个 pandas dataframe df:
times = pd.date_range(start="2018-09-09",end="2020-02-02")
values = np.random.rand(512)
# Make df
df = pd.DataFrame({'Time' : times,
'Value': values})
And I can plot this easily using plt.plot:我可以使用 plt.plot 轻松实现 plot:
But now I want to add a trendline.但现在我想添加一条趋势线。 I tried using some answers:我尝试使用一些答案:
How can I draw scatter trend line on matplot? 如何在 matplot 上绘制散点趋势线? Python-Pandas Python-熊猫
Which doesn't work:哪个不起作用:
TypeError: unsupported operand type(s) for +: 'datetime.datetime' and 'float'
Then I found the following question and answer:然后我找到了以下问题和答案:
TypeError: ufunc subtract cannot use operands with types dtype('<M8[ns]') and dtype('float64') 类型错误:ufunc 减法不能使用类型为 dtype('<M8[ns]') 和 dtype('float64') 的操作数
But these don't work as well.但这些也不起作用。 There my understanding of the issue stops, and I can't find anything else.我对这个问题的理解停止了,我找不到其他任何东西。
My code so far:到目前为止我的代码:
# Get values for the trend line analysis
x = df['Time'].dt.to_pydatetime()
# Calculate a fit line
trend = np.polyfit(x, df['Value'], 1)
fit = np.poly1d(trend)
# General plot again
figure(figsize=(12, 8))
plt.plot(x, df['Value'])
plt.xlabel('Date')
plt.ylabel('Value')
# Now trendline
plt.plot(x, fit(x), "r--")
# And show
plt.show()
One approach is to convert the dates using matplotlib's date2num() function and its counterpart the num2date function:一种方法是使用 matplotlib 的date2num() function 及其对应的num2date function 转换日期:
import matplotlib.pyplot as plt
import pandas as pd
import numpy as np
import matplotlib.dates as dates
np.random.seed(123)
times = pd.date_range(start="2018-09-09",end="2020-02-02")
values = np.random.rand(512)
df = pd.DataFrame({'Time' : times,
'Value': values})
# Get values for the trend line analysis
x_dates = df['Time']
x_num = dates.date2num(x_dates)
# Calculate a fit line
trend = np.polyfit(x_num, df['Value'], 1)
fit = np.poly1d(trend)
# General plot again
#figure(figsize=(12, 8))
plt.plot(x_dates, df['Value'])
plt.xlabel('Date')
plt.ylabel('Value')
# Not really necessary to convert the values back into dates
#but added as a demonstration in case one wants to plot non-linear curves
x_fit = np.linspace(x_num.min(), x_num.max())
plt.plot(dates.num2date(x_fit), fit(x_fit), "r--")
# And show
plt.show()
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