matplotlib · efiring · Mar 17, 2012 · Feb 27, 2012 · Feb 27, 2012 · Feb 27, 2012
diff --git a/examples/widgets/lasso_selector_demo.py b/examples/widgets/lasso_selector_demo.py
@@ -0,0 +1,82 @@
+import numpy as np
+
+from matplotlib.widgets import LassoSelector
+from matplotlib.path import Path
+
+
+class SelectFromCollection(object):
+    """Select indices from a matplotlib collection using `LassoSelector`.
+
+    Selected indices are saved in the `ind` attribute. This tool highlights
+    selected points by fading them out (i.e., reducing their alpha values).
+    If your collection has alpha < 1, this tool will permanently alter them.
+
+    Note that this tool selects collection objects based on their *origins*
+    (i.e., `offsets`).
+
+    Parameters
+    ----------
+    ax : :class:`~matplotlib.axes.Axes`
+        Axes to interact with.
+
+    collection : :class:`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).reshape(self.Npts, -1)
+
+        self.lasso = LassoSelector(ax, onselect=self.onselect)
+        self.ind = []
+
+    def onselect(self, verts):
+        path = Path(verts)
+        self.ind = np.nonzero([path.contains_point(xy) for xy in self.xys])[0]
+        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.lasso.disconnect_events()
+        self.fc[:, -1] = 1
+        self.collection.set_facecolors(self.fc)
+        self.canvas.draw_idle()
+
+
+if __name__ == '__main__':
+    import matplotlib.pyplot as plt
+
+    plt.ion()
+    data = np.random.rand(100, 2)
+
+    subplot_kw = dict(xlim=(0,1), ylim=(0,1), autoscale_on=False)
+    fig, ax = plt.subplots(subplot_kw=subplot_kw)
+
+    pts = ax.scatter(data[:, 0], data[:, 1], s=80)
+    selector = SelectFromCollection(ax, pts)
+
+    plt.draw()
+    raw_input('Press any key to accept selected points')
+    print "Selected points:"
+    print selector.xys[selector.ind]
+    selector.disconnect()
+
+    # Block end of script so you can check that the lasso is disconnected.
+    raw_input('Press any key to quit')
+