如何将过滤器应用于局部最大值（绘图）答案

【问题标题】：How to apply filter to local maxima (plot)如何将过滤器应用于局部最大值（绘图）
【发布时间】：2019-04-28 10:06:57
【问题描述】：

下面的代码让我绘制 trc-oscilloscope 数据。此外，我正在标记绘图的局部最大值和最小值。

import matplotlib.pyplot as plt
import pandas as pd
import readTrc
import numpy as np
from scipy.signal import argrelextrema
from scipy import signal

#100mil datapoints
datX, datY, m = readTrc.readTrc('C220180104_ch2_UHF00014.trc')
srx, sry = pd.Series(datX * 1000), pd.Series(datY * 1000)
df = pd.concat([srx, sry], axis = 1)
df.set_index(0, inplace = True)

#Impulse location
x1 = df[1].idxmax() - 0.0005
x2 = df[1].idxmax() + 0.003
df2 = df.loc[x1:x2]

#Locate Maximum
print('Maximum at:', round(df[1].idxmax(), 6), 'ms')

#Local Maxima
n=10 #Every n maximum a Point will be placed
df3_min = df2.iloc[argrelextrema(df2[1].values, np.less_equal, order=n)[0]][1]
df3_max = df2.iloc[argrelextrema(df2[1].values, np.greater_equal, order=n)[0]][1]
plt.scatter(df3_min.index, df3_min, c='r')
plt.scatter(df3_max.index, df3_max, c='g')

#Plot Impulse
df2[1].plot(grid = 1,
        linewidth = 1,
        figsize = (9,5),
        color = 'blue',
        legend = False,
        xlim = (x1, x2))

plt.xlabel('Time in ms')
plt.ylabel('UHF-Signal in mV')
plt.show()

输出：

现在我想通过最大值绘制一条曲线。我该怎么做？我尝试使用过滤器，但它们“切断”了最高极值（最大值）。

编辑：

添加这些代码连接最大值：

df3_max.plot()

输出：

现在如果我尝试应用黄油过滤器：

b, a = signal.butter(5, 0.1)
y2 = signal.filtfilt(b,a, df3_max[1].values)
df3_max = pd.DataFrame(y2, index=df3_max.index)

我得到一个错误：

Traceback (most recent call last):
  File "/home/artur/.local/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 3078, in get_loc
    return self._engine.get_loc(key)
  File "pandas/_libs/index.pyx", line 140, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/index.pyx", line 162, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/hashtable_class_helper.pxi", line 379, in pandas._libs.hashtable.Float64HashTable.get_item
  File "pandas/_libs/hashtable_class_helper.pxi", line 385, in pandas._libs.hashtable.Float64HashTable.get_item
KeyError: 1.0

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/artur/Desktop/shard_plot/UHF_impulse_plot.py", line 38, in <module>
    y2 = signal.filtfilt(b,a, df3_max[1].values)
  File "/home/artur/.local/lib/python3.6/site-packages/pandas/core/series.py", line 767, in __getitem__
    result = self.index.get_value(self, key)
  File "/home/artur/.local/lib/python3.6/site-packages/pandas/core/indexes/numeric.py", line 358, in get_value
    loc = self.get_loc(k)
  File "/home/artur/.local/lib/python3.6/site-packages/pandas/core/indexes/numeric.py", line 419, in get_loc
    tolerance=tolerance)
  File "/home/artur/.local/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 3080, in get_loc
    return self._engine.get_loc(self._maybe_cast_indexer(key))
  File "pandas/_libs/index.pyx", line 140, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/index.pyx", line 162, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/hashtable_class_helper.pxi", line 379, in pandas._libs.hashtable.Float64HashTable.get_item
  File "pandas/_libs/hashtable_class_helper.pxi", line 385, in pandas._libs.hashtable.Float64HashTable.get_item
KeyError: 1.0

【问题讨论】：

plot 函数不能满足您的需要吗？ plt.plot(df3_max.index, df3_max) 甚至 df3_max.plot()？不过我可能不明白这个问题。
除了plt.scatter(df3_max.index, df3_max, c='g')，您还可以绘制plt.plot(df3_max.index, df3_max, c='g')。这是否已经解决了它，还是您的意思是通过您的最大值进行一些样条拟合？
df3_max 是一个数据框，除了最大值之外，没有填充。我不得不这样做是因为我要绘制的最大值（圆圈）必须与基本 df 具有相同的索引。
我不知道你的数据框的格式，但似乎你只需要df3_max 而不是df3_max[1]。
@busybear：你可能想添加这个作为答案:)

标签： python pandas numpy matplotlib scipy

【解决方案1】：

plot 的最大值方法 df3_max 应该可以解决问题：

df3_max.plot()

要应用过滤器，您可以将scipy.signal.butter 函数用于低通过滤器。

b, a = signal.butter(5, 0.1)
y2 = signal.filtfilt(b, a, df3_max.values)
df3_max_filt = pd.DataFrame(y2, index=df3_max.index)

df3_max_filt.plot()

【讨论】：