当将x和y值指定为numpy数组时,找到所有局部的Maxima和Minima [英] Find all local Maxima and Minima when x and y values are given as numpy arrays
问题描述
我有两个数组x
和y
作为:
x = np.array([6, 3, 5, 2, 1, 4, 9, 7, 8])
y = np.array([2, 1, 3, 5, 3, 9, 8, 10, 7])
我正在找到局部最小值和最大值的索引,如下所示:
I am finding index of local minima and maxima as follows:
sortId = np.argsort(x)
x = x[sortId]
y = y[sortId]
minm = np.array([])
maxm = np.array([])
while i < y.size-1:
while(y[i+1] >= y[i]):
i = i + 1
maxm = np.insert(maxm, 0, i)
i++
while(y[i+1] <= y[i]):
i = i + 1
minm = np.insert(minm, 0, i)
i++
此代码中的问题是什么?
答案应该是minima = [2, 5, 7]
的索引
和maxima = [1, 3, 6]
.
What is the problem in this code?
The answer should be index of minima = [2, 5, 7]
and that of maxima = [1, 3, 6]
.
推荐答案
您根本不需要此while
循环.下面的代码将为您提供所需的输出;它找到所有局部最小值和所有局部最大值,并将它们分别存储在minm
和maxm
中.请注意:将其应用于大型数据集时,请确保先平滑信号;否则,请确保平滑.否则,您将陷入无数的极端.
You do not need this while
loop at all. The code below will give you the output you want; it finds all local minima and all local maxima and stores them in minm
and maxm
, respectively. Please note: When you apply this to large datasets, make sure to smooth the signals first; otherwise you will end up with tons of extrema.
import numpy as np
from scipy.signal import argrelextrema
import matplotlib.pyplot as plt
x = np.array([6, 3, 5, 2, 1, 4, 9, 7, 8])
y = np.array([2, 1, 3 ,5 ,3 ,9 ,8, 10, 7])
# sort the data in x and rearrange y accordingly
sortId = np.argsort(x)
x = x[sortId]
y = y[sortId]
# this way the x-axis corresponds to the index of x
plt.plot(x-1, y)
plt.show()
maxm = argrelextrema(y, np.greater) # (array([1, 3, 6]),)
minm = argrelextrema(y, np.less) # (array([2, 5, 7]),)
这应该比上面的while
循环高效得多.
This should be far more efficient than the above while
loop.
情节看起来像这样;我移动了x值,使其与minm
和maxm
)中返回的索引相对应:
The plot looks like this; I shifted the x-values so that they correspond to the returned indices in minm
and maxm
):
从SciPy 1.1版开始,您还可以使用 find_peaks :
As of SciPy version 1.1, you can also use find_peaks:
from scipy.signal import find_peaks
peaks, _ = find_peaks(y)
# this way the x-axis corresponds to the index of x
plt.plot(x-1, y)
plt.plot(peaks, y[peaks], "x")
plt.show()
这产生了
令人高兴的是,您现在还可以轻松设置最小峰高(例如8):
The nice thing is, that you can now also easily also set a minimum peak height (e.g. 8):
peaks, _ = find_peaks(y, height=8)
# this way the x-axis corresponds to the index of x
plt.plot(x-1, y)
plt.plot(peaks, y[peaks], "x")
plt.show()
请注意,现在排除了第一个峰,因为其高度低于8.
Note that now the first peak is excluded as its height is below 8.
此外,您还可以设置峰之间的最小距离(例如5个):
Furthermore, you can set also the minimal distance between peaks (e.g. 5):
peaks, _ = find_peaks(y, distance=5)
# this way the x-axis corresponds to the index of x
plt.plot(x-1, y)
plt.plot(peaks, y[peaks], "x")
plt.show()
现在排除了中间峰,因为它与其他两个峰的距离小于5.
Now the middle peak is excluded as its distance to the other two peaks is less than 5.
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