Select indices from a collection using polygon selector#
Shows how one can select indices of a polygon interactively.
import numpy as np from matplotlib.path import Path from matplotlib.widgets import PolygonSelector class SelectFromCollection: """ Select indices from a matplotlib collection using `PolygonSelector`. Selected indices are saved in the `ind` attribute. This tool fades out the points that are not part of the selection (i.e., reduces their alpha values). If your collection has alpha < 1, this tool will permanently alter the alpha values. Note that this tool selects collection objects based on their *origins* (i.e., `offsets`). Parameters ---------- ax : `~matplotlib.axes.Axes` Axes to interact with. collection : `matplotlib.collections.Collection` subclass Collection you want to select from. alpha_other : 0 <= float <= 1 To highlight a selection, this tool sets all selected points to an alpha value of 1 and non-selected points to *alpha_other*. """ def __init__(self, ax, collection, alpha_other=0.3): self.canvas = ax.figure.canvas self.collection = collection self.alpha_other = alpha_other self.xys = collection.get_offsets() self.Npts = len(self.xys) # Ensure that we have separate colors for each object self.fc = collection.get_facecolors() if len(self.fc) == 0: raise ValueError('Collection must have a facecolor') elif len(self.fc) == 1: self.fc = np.tile(self.fc, (self.Npts, 1)) self.poly = PolygonSelector(ax, self.onselect, draw_bounding_box=True) self.ind =  def onselect(self, verts): path = Path(verts) self.ind = np.nonzero(path.contains_points(self.xys)) self.fc[:, -1] = self.alpha_other self.fc[self.ind, -1] = 1 self.collection.set_facecolors(self.fc) self.canvas.draw_idle() def disconnect(self): self.poly.disconnect_events() self.fc[:, -1] = 1 self.collection.set_facecolors(self.fc) self.canvas.draw_idle() if __name__ == '__main__': import matplotlib.pyplot as plt fig, ax = plt.subplots() grid_size = 5 grid_x = np.tile(np.arange(grid_size), grid_size) grid_y = np.repeat(np.arange(grid_size), grid_size) pts = ax.scatter(grid_x, grid_y) selector = SelectFromCollection(ax, pts) print("Select points in the figure by enclosing them within a polygon.") print("Press the 'esc' key to start a new polygon.") print("Try holding the 'shift' key to move all of the vertices.") print("Try holding the 'ctrl' key to move a single vertex.") plt.show() selector.disconnect() # After figure is closed print the coordinates of the selected points print('\nSelected points:') print(selector.xys[selector.ind])
Select points in the figure by enclosing them within a polygon. Press the 'esc' key to start a new polygon. Try holding the 'shift' key to move all of the vertices. Try holding the 'ctrl' key to move a single vertex. Selected points: 
The use of the following functions, methods, classes and modules is shown in this example: