Adds errors in charts

pygal/graph/bar.py

@@ -82,6 +82,18 @@ class Bar(Graph):
             x_center, y_center = self._bar(
                 bar, x, y, index, i, self.zero, secondary=rescale,
                 rounded=serie.rounded_bars)
+
+            errors = metadata.get('errors') if metadata else None
+            if errors:
+                error_node = self.svg.node(bar, class_='errors')
+                base_x = x_center
+                transpose = ident
+                if self.horizontal:
+                    transpose = swap
+                    base_x = y_center
+                self.svg.draw_errors(error_node, errors, base_x,
+                                     transpose=transpose)
+
             self._tooltip_data(
                 bar, val, x_center, y_center, classes="centered")
             self._static_value(serie_node, val, x_center, y_center)

pygal/graph/line.py

@@ -103,7 +103,8 @@ class Line(Graph):
                     self.svg.node(serie_node['overlay'], class_="dots"),
                     metadata)
                 val = self._get_value(serie.points, i)
-                self.svg.node(dots, 'circle', cx=x, cy=y, r=serie.dots_size,
+                self.svg.node(dots, 'circle', cx=x, cy=y,
+                                    r=serie.dots_size,
                                     class_='dot reactive tooltip-trigger')
                 self._tooltip_data(
                     dots, val, x, y)
@@ -112,6 +113,11 @@ class Line(Graph):
                     x + self.value_font_size,
                     y + self.value_font_size)
 
+                errors = metadata.get('errors') if metadata else None
+                if errors:
+                    error_node = self.svg.node(dots, class_='errors')
+                    self.svg.draw_errors(error_node, errors, x)
+
         if serie.stroke:
             if self.interpolate:
                 view_values = list(map(self.view, serie.interpolated))

pygal/svg.py

@@ -30,7 +30,7 @@ from datetime import date, datetime
 from numbers import Number
 from lxml import etree
 from math import cos, sin, pi
-from pygal.util import template, coord_format, minify_css
+from pygal.util import template, coord_format, minify_css, ident
 from pygal import __version__
 
 
@@ -240,3 +240,33 @@ class Svg(object):
         if self.graph.disable_xml_declaration or is_unicode:
             svg = svg.decode('utf-8')
         return svg
+
+    def draw_errors(self, node, errors, base_x, transpose=None):
+        """Draws the confidence level for a given point."""
+        if not transpose:
+            transpose = ident
+        width = (self.graph.view.x(1) - self.graph.view.x(0)) / self.graph._len
+        series_margin = width * getattr(self.graph, '_series_margin', 0)
+        width -= 2 * series_margin
+        offset = (width - width / 2) / 2
+
+        lower_tip = transpose((base_x, self.graph.view.y(errors.get('min'))))
+        upper_tip = transpose((base_x, self.graph.view.y(errors.get('max'))))
+
+        lower_left_tip = transpose((base_x - offset,
+                                   self.graph.view.y(errors.get('min'))))
+        lower_right_tip = transpose((base_x + offset,
+                                    self.graph.view.y(errors.get('min'))))
+
+        upper_left_tip = transpose((base_x - offset,
+                                   self.graph.view.y(errors.get('max'))))
+        upper_right_tip = transpose((base_x + offset,
+                                    self.graph.view.y(errors.get('max'))))
+
+        # base line
+        self.line(node, coords=[lower_tip, upper_tip], class_='error')
+        # hat/foot
+        self.line(node, coords=[lower_left_tip, lower_right_tip],
+                  class_='error')
+        self.line(node, coords=[upper_left_tip, upper_right_tip],
+                  class_='error')

pygal/util.py

@@ -24,7 +24,7 @@ from __future__ import division
 from pygal._compat import to_str, u, is_list_like
 import re
 from decimal import Decimal
-from math import floor, pi, log, log10, ceil
+from math import floor, pi, log, log10, ceil, fsum, sqrt
 from itertools import cycle
 from functools import reduce
 from pygal.adapters import not_zero, positive
@@ -228,7 +228,7 @@ def get_texts_box(texts, fs):
 
 
 def decorate(svg, node, metadata):
-    """Add metedata next to a node"""
+    """Add metadata next to a node"""
     if not metadata:
         return node
     xlink = metadata.get('xlink')
@@ -376,6 +376,13 @@ def prepare_values(raw, config, cls):
             if isinstance(raw_value, dict):
                 raw_value = dict(raw_value)
                 value = raw_value.pop('value', None)
+                if not value:
+                    stdd = raw_value.pop('stdd', None)
+                    errors = raw_value.pop('errors', None)
+                    if stdd and is_list_like(stdd):
+                        value = mean(stdd)
+                        if not errors:
+                            raw_value.update(dict(errors=compute_errors(stdd)))
                 metadata[index] = raw_value
             else:
                 value = raw_value
@@ -423,3 +430,25 @@ def split_title(title, width, title_fs):
             title_line = title_line[i:].strip()
         titles.append(title_line)
     return titles
+
+
+def mean(values):
+    """Return the mean of a serie of values."""
+    return fsum(values) / len(values)
+
+
+def variance(values):
+    """Return the variance of a serie of values."""
+    values_mean = mean(values)
+    return fsum((v-values_mean) ** 2 for v in values) / len(values)
+
+
+def std_deviation(values):
+    """Returns the standard deviation of values."""
+    return sqrt(variance(values))
+
+
+def compute_errors(values):
+    m = mean(values)
+    stdd = std_deviation(values)
+    return dict(mean=m, min=m-stdd, max=m+stdd)