Added new mode to box plot chart: "extremes". Which will use the minimum and the maximum values as q0 and q4, respectively.

pygal/graph/box.py

@@ -159,10 +159,15 @@ class Box(Graph):
             sum(quartiles) / len(quartiles)))
 
     @staticmethod
-    def _box_points(values):
+    def _box_points(values, mode='1.5IQR'):
         """
-        Return a 5-tuple of Q1 - 1.5 * IQR, Q1, Median, Q3,
+        Default mode: (mode='1.5IQR' or unset)
+            Return a 5-tuple of Q1 - 1.5 * IQR, Q1, Median, Q3,
         and Q3 + 1.5 * IQR for a list of numeric values.
+        Extremes mode: (mode='extremes')
+            Return a 5-tuple of minimum, Q1, Median, Q3,
+        and maximum for a list of numeric values.
+
 
         The iterator values may include None values.
 
@@ -202,6 +207,10 @@ class Box(Graph):
                     q3 = 0.25 * s[3*m+1] + 0.75 * s[3*m+2]
 
             iqr = q3 - q1
-            q0 = q1 - 1.5 * iqr
-            q4 = q3 + 1.5 * iqr
+            if mode == 'extremes':
+                q0 = min(s)
+                q4 = max(s)
+            else:
+                q0 = q1 - 1.5 * iqr
+                q4 = q3 + 1.5 * iqr
             return q0, q1, q2, q3, q4

pygal/test/test_box.py

@@ -49,6 +49,35 @@ def test_quartiles():
     assert q3 == 4
     assert q4 == 4
 
+def test_quartiles_min_extremes():
+    a = [-2.0, 3.0, 4.0, 5.0, 8.0]  # odd test data
+    q0, q1, q2, q3, q4 = Box._box_points(a, mode='extremes')
+
+    assert q1 == 7.0 / 4.0
+    assert q2 == 4.0
+    assert q3 == 23 / 4.0
+    assert q0 == -2.0  # min
+    assert q4 == 8.0  # max
+
+    b = [1.0, 4.0, 6.0, 8.0]  # even test data
+    q0, q1, q2, q3, q4 = Box._box_points(b, mode='extremes')
+
+    assert q2 == 5.0
+
+    c = [2.0, None, 4.0, 6.0, None]  # odd with None elements
+    q0, q1, q2, q3, q4 = Box._box_points(c, mode='extremes')
+
+    assert q2 == 4.0
+
+    d = [4]
+    q0, q1, q2, q3, q4 = Box._box_points(d, mode='extremes')
+
+    assert q0 == 4
+    assert q1 == 4
+    assert q2 == 4
+    assert q3 == 4
+    assert q4 == 4
+
 
 def test_simple_box():
     box = ghostedBox()