Question

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:

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

Answer 1

您可以使用pandas附带的插值功能。由于您的数据框已经为每个索引都有一个值，您可以使用更稀疏的索引填充它，并使用NaN值填充每个以前不存在的索引。然后，在选择多个插值methods available之一后，插入并绘制数据：

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()

Answer 2

有一种解决方法，我们将创建两个图 - 1) 非平滑/带有日期标签的插值 2) 不带日期标签的平滑。

使用参数 linestyle=" " 绘制 1) 并将要绘制在 x 轴上的日期转换为字符串类型。

使用参数 linestyle="-" 绘制 2) 并分别使用 np.linespace 和 make_interp_spline 对 x 轴和 y 轴进行插值。

以下是针对您的代码使用所讨论的解决方法。

# your initial code
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
from scipy.interpolate import make_interp_spline
%matplotlib inline
startDate = "2015-05-15"
endDate = "2015-07-5" #reduced the end date so smoothness is clearly seen
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)
fig, axs = plt.subplots(1, 1, figsize=(40, 12))
x = df.index
y = df.value

# workaround by creating linespace for length of your x axis
x_new = np.linspace(0, len(df.index), 300)
a_BSpline = make_interp_spline(
    [i for i in range(0, len(df.index))],
    df.value,
    k=5,
)
y_new = a_BSpline(x_new)

# plot this new plot with linestyle = "-"
axs.plot(
    x_new[:-5], # removing last 5 entries to remove noise, because interpolation outputs large values at the end.
    y_new[:-5],
    "-",
    label="interpolated"
)

# to get the date on x axis we will keep our previous plot but linestyle will be None so it won't be visible
x = list(x.astype(str))
axs.plot(x, y, linestyle=" ", alpha=0.75, label="initial")
xt = [x[i] for i in range(0,len(x),5)]
plt.xticks(xt,rotation="vertical")
plt.legend()
fig.show()

结果图

重叠图以查看平滑。

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

2 个答案: