在茎图中使用交互小部件

Question

我正在尝试在Jupyter笔记本中绘制Python stem图。

情节是这样的：

%matplotlib inline
import matplotlib.pyplot as plt
import numpy as np
from scipy import fftpack

f = 10  
f_s = 100  
t = np.linspace(0, 2, 2 * f_s, endpoint=False)
x = np.sin(f * 2 * np.pi * t)

X = fftpack.fft(x)
freqs = fftpack.fftfreq(len(x)) * f_s 

fig, ax = plt.subplots()
ax.stem(freqs, np.abs(X))
ax.set_xlabel('Frecuency [Hz]')
ax.set_ylabel('Spectrum')
ax.set_xlim(-f_s / 2, f_s / 2)
ax.set_ylim(-5, 110);

我想像本文Jupyter Notebook: interactive plot with widgets 一样添加一个滑块。 这篇文章中的解决方案

%matplotlib inline
import matplotlib.pyplot as plt
import numpy as np
from scipy import fftpack
from ipywidgets import *

f = 10  
f_s = 100  
t = np.linspace(0, 2, 2 * f_s, endpoint=False)
x = np.sin(f * 2 * np.pi * t)

X = fftpack.fft(x)
freqs = fftpack.fftfreq(len(x)) * f_s 
fig, ax = plt.subplots()
line, = ax.stem(freqs, np.abs(X))
ax.set_xlabel('Frecuency [Hz]')
ax.set_ylabel('Spectrum')
ax.set_xlim(-f_s / 2, f_s / 2)
ax.set_ylim(-5, 110);

def update(f_s=100):
    line.set_ydata(fftpack.fftfreq(len(x)) * f_s)
    ax.set_xlim(-f_s / 2, f_s / 2)
    fig.canvas.draw()

interact(update);

返回一个错误：

     ValueError                                Traceback (most recent call last)
<ipython-input-18-fd1aaf0ca96d> in <module>()
      7 
      8 fig, ax = plt.subplots()
----> 9 line, = ax.stem(freqs, np.abs(X))
     10 ax.set_xlabel('Frecuency [Hz]')
     11 ax.set_ylabel('Spectrum')

ValueError: too many values to unpack (expected 1)

Answer 1

我认为您要展示的内容最重要。如果更改频率，则可能还需要重新计算频谱。因此，我们首先使用线图对其进行更正。

%matplotlib notebook
import matplotlib.pyplot as plt
import numpy as np
from scipy import fftpack
from ipywidgets import *

def func(f_s):
    t = np.linspace(0, 2, 2 * f_s, endpoint=False)
    x = np.sin(f * 2 * np.pi * t)
    X = fftpack.fft(x)
    freqs = fftpack.fftfreq(len(x)) * f_s 
    return freqs, np.abs(X)

f = 10
f_s = 100  

fig, ax = plt.subplots()
line, = ax.plot(*func(f_s), marker="o")
ax.set_xlabel('Frecuency [Hz]')
ax.set_ylabel('Spectrum')
ax.set_xlim(-f_s / 2, f_s / 2)
ax.set_ylim(-5, 110);

def update(f_s=100):
    if f_s > 0:
        x, y = func(f_s)
        line.set_data(x, y)
        ax.set_xlim(-f_s / 2, f_s / 2)
        ax.set_ylim(None, 1.1*y.max())
        fig.canvas.draw()

interact(update);

现在stem绘图的问题在于，它将创建许多需要更新的行。因此，我宁愿建议使用LineCollection。

%matplotlib notebook
import matplotlib.pyplot as plt
from matplotlib.collections import LineCollection
import numpy as np
from scipy import fftpack
from ipywidgets import *

def func(f_s):
    t = np.linspace(0, 2, 2 * f_s, endpoint=False)
    x = np.sin(f * 2 * np.pi * t)
    X = fftpack.fft(x)
    freqs = fftpack.fftfreq(len(x)) * f_s 
    return freqs, np.abs(X)

f = 10
f_s = 100  

fig, ax = plt.subplots()
x,y = func(f_s)
markers, = ax.plot(x,y, ls="none", marker="o")
baseline = ax.axhline(0, color="crimson")

verts=np.c_[x, np.zeros_like(x), x, y].reshape(len(x),2,2)
col = LineCollection(verts)
ax.add_collection(col)

ax.set_xlabel('Frecuency [Hz]')
ax.set_ylabel('Spectrum')
ax.set_xlim(-f_s / 2, f_s / 2)
ax.set_ylim(None, 110);

def update(f_s=100):
    if f_s > 0:
        x, y = func(f_s)
        markers.set_data(x, y)
        verts=np.c_[x, np.zeros_like(x), x, y].reshape(len(x),2,2)
        col.set_segments(verts)
        ax.set_xlim(-f_s / 2, f_s / 2)
        ax.set_ylim(None, 1.1*y.max())
        fig.canvas.draw_idle()

interact(update);