new stdev and pstdev modes of Box plot

pygal/config.py

@@ -344,7 +344,8 @@ class Config(CommonConfig):
     mode = Key(
         None, str, "Value", "Sets the mode to be used. "
         "(Currently only supported on box plot)",
-        "May be %s" % ' or '.join(["1.5IQR", "extremes", "tukey"]))
+        "May be %s" % ' or '.join(["1.5IQR", "extremes", "tukey", "stdev",\
+            "pstdev"]))
 
     order_min = Key(
         None, int, "Value", "Minimum order of scale, defaults to None")

pygal/graph/box.py

@@ -51,7 +51,7 @@ class Box(Graph):
                 if self.mode == "extremes":
                     return 'Min: %s Q1: %s Q2: %s Q3: %s Max: %s' \
                         % tuple(map(sup, x[1:6]))
-                elif self.mode == "tukey":
+                elif self.mode in ["tukey", "stdev", "pstdev"]:
                     return 'Min: %s Lower Whisker: %s Q1: %s Q2: %s Q3: %s '\
                         'Upper Whisker: %s Max: %s' % tuple(map(sup, x))
                 else:
@@ -195,8 +195,15 @@ class Box(Graph):
         Extremes mode: (mode='extremes')
             Return a 7-tuple of 2x minimum, Q1, Median, Q3,
         and 2x maximum for a list of numeric values.
-        Outliers (Tukey) mode: (mode='tukey')
+        Tukey mode: (mode='tukey')
             Return a 7-tuple of min, q[0..4], max and a list of outliers
+        Outliers are considered values x: x < q1 - IQR or x > q3 + IQR
+        SD mode: (mode='stdev')
+            Return a 7-tuple of min, q[0..4], max and a list of outliers
+        Outliers are considered values x: x < q2 - SD or x > q2 + SD
+        SDp mode: (mode='pstdev')
+            Return a 7-tuple of min, q[0..4], max and a list of outliers
+        Outliers are considered values x: x < q2 - SDp or x > q2 + SDp
 
 
         The iterator values may include None values.
@@ -212,6 +219,21 @@ class Box(Graph):
             else:  # seq has an odd length
                 return seq[n // 2]
 
+        def mean(seq):
+            return sum(seq) /len(seq)
+
+        def stdev(seq):
+            m = mean(seq)
+            l = len(seq)
+            v = sum((n - m)**2 for n in seq) / (l - 1) # variance
+            return v**0.5 # sqrt
+
+        def pstdev(seq):
+            m = mean(seq)
+            l = len(seq)
+            v = sum((n - m)**2 for n in seq) / l # variance
+            return v**0.5 # sqrt
+
         outliers = []
         # sort the copy in case the originals must stay in original order
         s = sorted([x for x in values if x is not None])
@@ -252,7 +274,25 @@ class Box(Graph):
                 q0 = s[b0]
                 q4 = s[b4-1]
                 outliers = s[:b0] + s[b4:]
-
+            elif mode == 'stdev':
+                # one standard deviation above and below the mean of the data
+                sd = stdev(s)
+                print s, sd
+                b0 = bisect_left(s, q2 - sd)
+                b4 = bisect_right(s, q2 + sd)
+                q0 = s[b0]
+                q4 = s[b4-1]
+                outliers = s[:b0] + s[b4:]
+            elif mode == 'pstdev':
+                # one population standard deviation above and below
+                # the mean of the data
+                sdp = pstdev(s)
+                print s, sd
+                b0 = bisect_left(s, q2 - sdp)
+                b4 = bisect_right(s, q2 + sdp)
+                q0 = s[b0]
+                q4 = s[b4-1]
+                outliers = s[:b0] + s[b4:]
             else:
                 q0 = q1 - 1.5 * iqr
                 q4 = q3 + 1.5 * iqr

pygal/test/test_box.py

@@ -113,7 +113,7 @@ def test_quartiles_tukey():
     assert max_s == 75
     assert outliers == [75]
 
-    # one more outlier, -30
+    # one more outlier, 77
     c = [6, 7, 15, 36, 39, 40, 41, 42, 43, 47, 49, 75, 77]
     (min_s, q0, q1, q2, q3, q4, max_s), outliers = Box._box_points(
         c, mode='tukey')
@@ -125,6 +125,18 @@ def test_quartiles_tukey():
     assert 75 in outliers
     assert 77 in outliers
 
+def test_quartiles_stdev():
+    a = [35, 42, 35, 41, 36, 6, 12, 51, 33, 27, 46, 36, 44, 53, 75, 46, 16,\
+        51, 45, 29, 25, 26, 54, 61, 27, 40, 23, 34, 51, 37]
+    SD = 14.67
+    (min_s, q0, q1, q2, q3, q4, max_s), outliers = Box._box_points(
+        a, mode='stdev')
+    assert min_s == min(a)
+    assert max_s == max(a)
+    assert q2 == 36.5
+    assert q4 <= q2 + SD
+    assert q0 >= q2 - SD
+    assert all(n in outliers for n in [6, 12, 16, 53, 54, 61, 75])
 
 def test_simple_box():
     box = ghostedBox()