如何在Matplotlib中刷新文本？

Question

我写了这段代码来读取Excel文件中的数据并绘制它们。对于特定的x值，我希望知道所有线的y值，因此我创建了一个滑块来更改这个x值，但我无法刷新打印y值的文本。

代码如下：

import numpy as np
from openpyxl import load_workbook as ld
import matplotlib
matplotlib.use('TkAgg')
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider

wb = ld(filename='example.xlsx')
data = wb['data']
time = wb['time']
row = data.max_row
column = data.max_column
x = np.ones((row, column))
y = np.ones((row, column))
result = np.ones(row)
for i in range(0, row):
    for j in range(0, column):

        x[i][j] = time.cell(row=i+1, column=j+1).value
        y[i][j] = data.cell(row=i+1, column=j+1).value


fig, ax = plt.subplots()
plt.subplots_adjust(left=0.25, bottom=0.25)
plt.plot(x[0], y[0], label='line1')
plt.plot(x[1], y[1], label='line2')
plt.plot(x[2], y[2], label='line3')
line, = plt.plot((np.amin(x), np.amin(x)), (np.amin(y), np.amax(y)))
plt.legend()
plt.grid(True)


axtime = plt.axes([0.25, 0.1, 0.65, 0.03])
stime = Slider(axtime, 'time', np.amin(x), np.amax(x), valinit=np.amin(x))


def y_text(r):
    ax.text(10, 8, str(r), style='italic')


def find(t):
    global x, y, result

    for i in range(0, row):
        for j in range(0, column):

            if x[i][j] == t or (t < x[i][j] and j == 0) or (t > x[i][j] and j == column):
                result[i] = y[i][j]
            elif x[i][j] < t < x[i][j+1]:
                result[i] = ((t-x[i][j])/(x[i][j+1]-x[i][j]))*(y[i][j+1]-y[i][j])+y[i][j]
    return result


def update(val):
    line.set_xdata(stime.val)
    find(stime.val)
    y_text(stime.val)
    fig.canvas.draw()
stime.on_changed(update)


plt.show()

结果如下所示：

正如您所看到的，文本被覆盖了。

- Leo

Answer 1

使用matplotlib小部件时，如果创建一个艺术家对象并调整其值（就像您在代码中对line进行的操作一样），则更新方法效果最佳。对于文本对象，您可以使用set_text和set_position方法更改其显示内容和位置。例如：

import numpy as np
import pylab as plt
from matplotlib.widgets import Slider

fig, ax = plt.subplots()
plt.subplots_adjust(bottom=0.25)
sax = plt.axes([0.25, 0.1, 0.65, 0.03])

x = np.linspace(0,2.*np.pi,100)
f = np.sin(x)
l, = ax.plot(x, f)

slider1 = Slider(sax, 'amplitude', -0.8, 0.8, valinit=0.8)

tpos = int(0.25*x.shape[0])
t1 = ax.text(x[tpos], f[tpos],  str(slider1.val))

tpos = int(0.75*x.shape[0])
t2 = ax.text(x[tpos], f[tpos],  str(slider1.val))

def update(val):
    f = slider1.val*np.sin(x)
    l.set_ydata(f)

    # update the value of the Text object
    tpos = int(0.25*x.shape[0])
    t1.set_position((x[tpos], f[tpos]))
    t1.set_text(str(slider1.val))

    tpos = int(0.75*x.shape[0])
    t2.set_position((x[tpos], f[tpos]))
    t2.set_text(str(slider1.val))

    plt.draw()

slider1.on_changed(update)
plt.show()

看起来像这样：

另一种选择可能是每次清除并重新绘制文本，但这样会更慢且更麻烦。

- Ed Smith