matplotlib · timhoffm · Aug 16, 2020 · Aug 11, 2020 · Aug 12, 2020 · Aug 12, 2020
diff --git a/examples/misc/packed_bubbles.py b/examples/misc/packed_bubbles.py
@@ -0,0 +1,171 @@
+"""
+===================
+Packed-bubble chart
+===================
+
+Create a packed-bubble chart to represent scalar data.
+The presented algorithm tries to move all bubbles as close to the center of
+mass as possible while avoiding some collisions by moving around colliding
+objects. In this example we plot the market share of different desktop
+browsers.
+(source: https://gs.statcounter.com/browser-market-share/desktop/worldwidev)
+"""
+
+import numpy as np
+import matplotlib.pyplot as plt
+
+browser_market_share = {
+    'browsers': ['firefox', 'chrome', 'safari', 'edge', 'ie', 'opera'],
+    'market_share': [8.61, 69.55, 8.36, 4.12, 2.76, 2.43],
+    'color': ['#5A69AF', '#579E65', '#F9C784', '#FC944A', '#F24C00', '#00B825']
+}
+
+
+class BubbleChart:
+    def __init__(self, area, bubble_spacing=0):
+        """
+        Setup for bubble collapse.
+
+        Parameters
+        ----------
+        area : array-like
+            Area of the bubbles.
+        bubble_spacing : float, default: 0
+            Minimal spacing between bubbles after collapsing.
+
+        Notes
+        -----
+        If "area" is sorted, the results might look weird.
+        """
+        area = np.asarray(area)
+        r = np.sqrt(area / np.pi)
+
+        self.bubble_spacing = bubble_spacing
+        self.bubbles = np.ones((len(area), 4))
+        self.bubbles[:, 2] = r
+        self.bubbles[:, 3] = area
+        self.maxstep = 2 * self.bubbles[:, 2].max() + self.bubble_spacing
+        self.step_dist = self.maxstep / 2
+
+        # calculate initial grid layout for bubbles
+        length = np.ceil(np.sqrt(len(self.bubbles)))
+        grid = np.arange(length) * self.maxstep
+        gx, gy = np.meshgrid(grid, grid)
+        self.bubbles[:, 0] = gx.flatten()[:len(self.bubbles)]
+        self.bubbles[:, 1] = gy.flatten()[:len(self.bubbles)]
+
+        self.com = self.center_of_mass()
+
+    def center_of_mass(self):
+        return np.average(
+            self.bubbles[:, :2], axis=0, weights=self.bubbles[:, 3]
+        )
+
+    def center_distance(self, bubble, bubbles):
+        return np.hypot(bubble[0] - bubbles[:, 0],
+                        bubble[1] - bubbles[:, 1])
+
+    def outline_distance(self, bubble, bubbles):
+        center_distance = self.center_distance(bubble, bubbles)
+        return center_distance - bubble[2] - \
+            bubbles[:, 2] - self.bubble_spacing
+
+    def check_collisions(self, bubble, bubbles):
+        distance = self.outline_distance(bubble, bubbles)
+        return len(distance[distance < 0])
+
+    def collides_with(self, bubble, bubbles):
+        distance = self.outline_distance(bubble, bubbles)
+        idx_min = np.argmin(distance)
+        return idx_min if type(idx_min) == np.ndarray else [idx_min]
+
+    def collapse(self, n_iterations=50):
+        """
+        Move bubbles to the center of mass.
+
+        Parameters
+        ----------
+        n_iterations : int, default: 50
+            Number of moves to perform.
+        """
+        for _i in range(n_iterations):
+            moves = 0
+            for i in range(len(self.bubbles)):
+                rest_bub = np.delete(self.bubbles, i, 0)
+                # try to move directly towards the center of mass
+                # direction vector from bubble to the center of mass
+                dir_vec = self.com - self.bubbles[i, :2]
+
+                # shorten direction vector to have length of 1
+                dir_vec = dir_vec / np.sqrt(dir_vec.dot(dir_vec))
+
+                # calculate new bubble position
+                new_point = self.bubbles[i, :2] + dir_vec * self.step_dist
+                new_bubble = np.append(new_point, self.bubbles[i, 2:4])
+
+                # check whether new bubble collides with other bubbles
+                if not self.check_collisions(new_bubble, rest_bub):
+                    self.bubbles[i, :] = new_bubble
+                    self.com = self.center_of_mass()
+                    moves += 1
+                else:
+                    # try to move around a bubble that you collide with
+                    # find colliding bubble
+                    for colliding in self.collides_with(new_bubble, rest_bub):
+                        # calculate direction vector
+                        dir_vec = rest_bub[colliding, :2] - self.bubbles[i, :2]
+                        dir_vec = dir_vec / np.sqrt(dir_vec.dot(dir_vec))
+                        # calculate orthagonal vector
+                        orth = np.array([dir_vec[1], -dir_vec[0]])
+                        # test which direction to go
+                        new_point1 = (self.bubbles[i, :2] + orth *
+                                      self.step_dist)
+                        new_point2 = (self.bubbles[i, :2] - orth *
+                                      self.step_dist)
+                        dist1 = self.center_distance(
+                            self.com, np.array([new_point1]))
+                        dist2 = self.center_distance(
+                            self.com, np.array([new_point2]))
+                        new_point = new_point1 if dist1 < dist2 else new_point2
+                        new_bubble = np.append(new_point, self.bubbles[i, 2:4])
+                        if not self.check_collisions(new_bubble, rest_bub):
+                            self.bubbles[i, :] = new_bubble
+                            self.com = self.center_of_mass()
+
+            if moves / len(self.bubbles) < 0.1:
+                self.step_dist = self.step_dist / 2
+
+    def plot(self, ax, labels, colors):
+        """
+        Draw the bubble plot.
+
+        Parameters
+        ----------
+        ax : matplotlib.axes.Axes
+        labels : list
+            Labels of the bubbles.
+        colors : list
+            Colors of the bubbles.
+        """
+        for i in range(len(self.bubbles)):
+            circ = plt.Circle(
+                self.bubbles[i, :2], self.bubbles[i, 2], color=colors[i])
+            ax.add_patch(circ)
+            ax.text(*self.bubbles[i, :2], labels[i],
+                    horizontalalignment='center', verticalalignment='center')
+
+
+bubble_chart = BubbleChart(area=browser_market_share['market_share'],
+                           bubble_spacing=0.1)
+
+bubble_chart.collapse()
+
+fig, ax = plt.subplots(subplot_kw=dict(aspect="equal"))
+bubble_chart.plot(
+    ax, browser_market_share['browsers'], browser_market_share['color'])
+ax.axis("off")
+ax.relim()
+ax.autoscale_view()
+ax.set_title('Browser market share')
+
+plt.show()