Initial commit of Box Plot

pygal/graph/__init__.py

@@ -39,5 +39,6 @@ CHARTS_NAMES = [
     'DateY',
     'Worldmap',
     'SupranationalWorldmap',
-    'Histogram'
+    'Histogram',
+    'Box'
 ]

pygal/graph/box.py

@@ -0,0 +1,146 @@
+# -*- coding: utf-8 -*-
+# This file is part of pygal
+#
+# A python svg graph plotting library
+# Copyright © 2012-2013 Kozea
+#
+# This library is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation, either version 3 of the License, or (at your option) any
+# later version.
+#
+# This library is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with pygal. If not, see <http://www.gnu.org/licenses/>.
+"""
+Box plot
+"""
+
+from __future__ import division
+from pygal.graph.graph import Graph
+from pygal.util import compute_scale, decorate
+
+
+class Box(Graph):
+    """
+    Box plot
+    For each series, shows the median value, the 25th and 75th percentiles, and the values within
+    1.5 times the interquartile range of the 25th and 75th percentiles.
+
+    See http://en.wikipedia.org/wiki/Box_plot
+    """
+    _series_margin = .06
+
+    def __init__(self, *args, **kwargs):
+        super(Box, self).__init__(*args, **kwargs)
+
+    def _compute(self):
+        """
+        Compute parameters necessary for later steps within the rendering process
+        """
+        # Note: this code was copied from Bar graph
+        if self._min:
+            self._box.ymin = min(self._min, self.zero)
+        if self._max:
+            self._box.ymax = max(self._max, self.zero)
+
+        x_pos = [
+            x / self._len for x in range(self._len + 1)
+        ] if self._len > 1 else [0, 1]  # Center if only one value
+
+        self._points(x_pos)
+
+        y_pos = compute_scale(
+            self._box.ymin, self._box.ymax, self.logarithmic, self.order_min
+        ) if not self.y_labels else map(float, self.y_labels)
+
+        self._x_labels = self.x_labels and list(zip(self.x_labels, [
+            (i + .5) / self._len for i in range(self._len)]))
+        self._y_labels = list(zip(map(self._format, y_pos), y_pos))
+
+    def _plot(self):
+        """
+        Plot the series data
+        """
+        for index, serie in enumerate(self.series):
+            self._boxf(self._serie(index), serie, index)
+
+    def _boxf(self, serie_node, serie, index):
+        """
+        For a specific series, draw the box plot.
+        """
+        # Note: q0 and q4 do not literally mean the zero-th quartile and the fourth quartile, but rather
+        # the distance from 1.5 times the inter-quartile range to Q1 and Q3, respectively.
+        q0, q1, q2, q3, q4 = self._box_points(serie.values)
+        boxes = self.svg.node(serie_node['plot'], class_="boxes")
+
+        metadata = serie.metadata.get(0)
+
+        box = decorate(
+            self.svg,
+            self.svg.node(boxes, class_='box'),
+            metadata)
+        val = self._format(q2)
+
+        x_center, y_center = self._draw_box(box, (q0, q1, q2, q3, q4), index)
+        self._tooltip_data(box, val, x_center, y_center, classes="centered")
+        #print(val)
+        #self._static_value(box, val, x_center, y_center)
+
+    def _draw_box(self, parent_node, quartiles, box_index):
+        """
+        Return the center of a bounding box defined by a box plot. Draws a box plot on self.svg.
+        """
+        width = (self.view.x(1) - self.view.x(0)) / self._len
+        #x, y = self.view((x, y))
+        series_margin = width * self._series_margin
+        #x += series_margin
+        width -= 2 * series_margin
+        #height = self.view.y(y_zero) - y
+        left_edge = self.view.x(0) + width * box_index
+
+        # draw lines for whiskers - bottom, median, and top
+        for whisker in (quartiles[0], quartiles[2], quartiles[4]):
+            self.svg.line(parent_node,
+                          coords=[(left_edge, self.view.y(whisker)), (left_edge + width, self.view.y(whisker))],
+                          attrib={'stroke-width': 3})
+
+        # box, bounded by Q1 and Q3
+        self.svg.node(parent_node,
+                      tag='rect',
+                      x=left_edge,
+                      y=self.view.y(quartiles[1]),
+                      height=self.view.y(quartiles[3]) - self.view.y(quartiles[1]),
+                      width=width,
+                      attrib={'fill-opacity': 0.25})
+
+        return (left_edge + width / 2, self.view.height / 2)
+
+    @staticmethod
+    def _box_points(values):
+        """
+        Return a 5-tuple of Q1 - 1.5 * IQR, Q1, Median, Q3, and Q3 + 1.5 * IQR for a list of numeric values
+
+        Uses quartile definition from  Mendenhall, W. and Sincich, T. L. Statistics for Engineering and the
+        Sciences, 4th ed. Prentice-Hall, 1995.
+        """
+        n = len(values)
+        if not n:
+            return 0, 0, 0, 0, 0
+        else:
+            s = sorted(values)  # sort the copy in case the originals must stay in original order
+            if n % 2 == 0:  # n is even
+                q2 = (values[n // 2] + values[n // 2 + 1]) / 2
+            else:
+                q2 = values[(n + 1) // 2]
+
+            q1 = values[int(round((n + 1) / 4))]
+            q3 = values[int(round((3 * n + 3) / 4))]
+            iqr = q3 - q1
+            q0 = q1 - 1.5 * iqr
+            q4 = q3 + 1.5 * iqr
+            return q0, q1, q2, q3, q4