matplotlib & pandas

Python/matplotlab/gallery/event_handling/resample.md

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+# 重采样数据
+
+下采样会降低信号的采样率或采样大小。在本教程中，当通过拖动和缩放调整打印时，将对信号进行缩减采样。
+
+![重采样数据示例](https://matplotlib.org/_images/sphx_glr_resample_001.png)
+
+```python
+import numpy as np
+import matplotlib.pyplot as plt
+
+
+# A class that will downsample the data and recompute when zoomed.
+class DataDisplayDownsampler(object):
+    def __init__(self, xdata, ydata):
+        self.origYData = ydata
+        self.origXData = xdata
+        self.max_points = 50
+        self.delta = xdata[-1] - xdata[0]
+
+    def downsample(self, xstart, xend):
+        # get the points in the view range
+        mask = (self.origXData > xstart) & (self.origXData < xend)
+        # dilate the mask by one to catch the points just outside
+        # of the view range to not truncate the line
+        mask = np.convolve([1, 1], mask, mode='same').astype(bool)
+        # sort out how many points to drop
+        ratio = max(np.sum(mask) // self.max_points, 1)
+
+        # mask data
+        xdata = self.origXData[mask]
+        ydata = self.origYData[mask]
+
+        # downsample data
+        xdata = xdata[::ratio]
+        ydata = ydata[::ratio]
+
+        print("using {} of {} visible points".format(
+            len(ydata), np.sum(mask)))
+
+        return xdata, ydata
+
+    def update(self, ax):
+        # Update the line
+        lims = ax.viewLim
+        if np.abs(lims.width - self.delta) > 1e-8:
+            self.delta = lims.width
+            xstart, xend = lims.intervalx
+            self.line.set_data(*self.downsample(xstart, xend))
+            ax.figure.canvas.draw_idle()
+
+
+# Create a signal
+xdata = np.linspace(16, 365, (365-16)*4)
+ydata = np.sin(2*np.pi*xdata/153) + np.cos(2*np.pi*xdata/127)
+
+d = DataDisplayDownsampler(xdata, ydata)
+
+fig, ax = plt.subplots()
+
+# Hook up the line
+d.line, = ax.plot(xdata, ydata, 'o-')
+ax.set_autoscale_on(False)  # Otherwise, infinite loop
+
+# Connect for changing the view limits
+ax.callbacks.connect('xlim_changed', d.update)
+ax.set_xlim(16, 365)
+plt.show()
+```
+
+## 下载这个示例
+            
+- [下载python源码: resample.py](https://matplotlib.org/_downloads/resample.py)
+- [下载Jupyter notebook: resample.ipynb](https://matplotlib.org/_downloads/resample.ipynb)