Python Matplotlib - Smooth plot line for x-axis with date values

问题

Im trying to smooth a graph line out but since the x-axis values are dates im having great trouble doing this. Say we have a dataframe as follows

import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
%matplotlib inline

startDate = '2015-05-15'
endDate = '2015-12-5'
index = pd.date_range(startDate, endDate)
data = np.random.normal(0, 1, size=len(index))
cols = ['value']

df = pd.DataFrame(data, index=index, columns=cols)

Then we plot the data

fig, axs = plt.subplots(1,1, figsize=(18,5))
x = df.index
y = df.value
axs.plot(x, y)
fig.show()

we get

Now to smooth this line there are some usefull staekoverflow questions allready like:

• Generating smooth line graph using matplotlib,
• Plot smooth line with PyPlot
• Creating numpy linspace out of datetime

But I just cant seem to get some code working to do this for my example, any suggestions?

回答1:

You can use interpolation functionality that is shipped with pandas. Because your dataframe has a value for every index already, you can populate it with an index that is more sparse, and fill every previously non-existent indices with NaN values. Then, after choosing one of many interpolation methods available, interpolate and plot your data:

index_hourly = pd.date_range(startDate, endDate, freq='1H')
df_smooth = df.reindex(index=index_hourly).interpolate('cubic')
df_smooth = df_smooth.rename(columns={'value':'smooth'})

df_smooth.plot(ax=axs, alpha=0.7)
df.plot(ax=axs, alpha=0.7)
fig.show()

来源：https://stackoverflow.com/questions/40559971/python-matplotlib-smooth-plot-line-for-x-axis-with-date-values