From d11aa40600442dfe3401351216333d84f21236b8 Mon Sep 17 00:00:00 2001
From: Jean-Marc Martins <jean-marc.martins@kozea.fr>
Date: Tue, 13 May 2014 12:20:10 +0200
Subject: [PATCH] Broken errors are broken

---
 pygal/config.py                      |   2 +
 pygal/css/style.css                  |   4 +
 pygal/graph/#box.py#                 | 208 +++++++++++++++++++++++++++
 pygal/graph/#pie.py#                 |  87 +++++++++++
 pygal/graph/bar.py                   |  24 +++-
 pygal/graph/base.py                  |  20 ++-
 pygal/graph/datey.py                 |  21 +--
 pygal/graph/frenchmap.py             |   6 +-
 pygal/graph/graph.py                 |  18 ++-
 pygal/graph/histogram.py             |  12 +-
 pygal/graph/line.py                  |  12 ++
 pygal/graph/stackedbar.py            |   6 +-
 pygal/graph/supranationalworldmap.py |   6 +-
 pygal/graph/verticalpyramid.py       |   5 +-
 pygal/graph/worldmap.py              |   8 +-
 pygal/graph/xy.py                    |   9 +-
 pygal/serie.py                       |  81 ++++++++++-
 pygal/svg.py                         |  29 ++++
 pygal/util.py                        |  14 +-
 19 files changed, 519 insertions(+), 53 deletions(-)
 create mode 100644 pygal/graph/#box.py#
 create mode 100644 pygal/graph/#pie.py#

diff --git a/pygal/config.py b/pygal/config.py
index 08f23c9..9f225cc 100644
--- a/pygal/config.py
+++ b/pygal/config.py
@@ -126,6 +126,8 @@ class Config(MetaConfig('ConfigBase', (object,), {})):
         None, str, "Look",
         "Graph Y-Axis title.", "Leave it to None to disable Y-Axis title.")
 
+    y_errors = Key(False, bool, "Look", "Set to True to display y-errors.")
+
     width = Key(
         800, int, "Look", "Graph width")
 
diff --git a/pygal/css/style.css b/pygal/css/style.css
index bc8f31e..5784964 100644
--- a/pygal/css/style.css
+++ b/pygal/css/style.css
@@ -129,6 +129,10 @@
   stroke-width: 10;
 }
 
+{{ id }}.err_marks .errors {
+  stroke: {{ style.foreground_dark }};
+}
+
 {{ colors }}
 
 
diff --git a/pygal/graph/#box.py# b/pygal/graph/#box.py#
new file mode 100644
index 0000000..de928e0
--- /dev/null
+++ b/pygal/graph/#box.py#
@@ -0,0 +1,208 @@
+# -*- coding: utf-8 -*-
+# This file is part of pygal
+#
+# A python svg graph plotting library
+# Copyright © 2012-2014 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
+from pygal._compat import is_list_like
+
+
+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)
+
+    @property
+    def _format(self):
+        """Return the value formatter for this graph"""
+        sup = super(Box, self)._format
+
+        def format_maybe_quartile(x):
+            if is_list_like(x):
+                if len(x) == 5:
+                    return 'Q1: %s Q2: %s Q3: %s' % tuple(map(sup, x[1:4]))
+            else:
+                return sup(x)
+        return format_maybe_quartile
+
+    def _compute(self):
+        """
+        Compute parameters necessary for later steps
+        within the rendering process
+        """
+        for serie in self.series:
+            serie.values = self._box_points(serie.values)
+
+        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 list(map(float, self.y_labels))
+
+        self._x_labels = self.x_labels and list(zip(self.x_labels, [
+            (i + .5) / self._order for i in range(self._order)]))
+        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.
+        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(serie.values)
+
+        x_center, y_center = self._draw_box(box, serie.values, index)
+        self._tooltip_data(box, val, x_center, y_center, classes="centered")
+        self._static_value(serie_node, 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._order
+        series_margin = width * self._series_margin
+        left_edge = self.view.x(0) + width * box_index + series_margin
+        width -= 2 * series_margin
+
+        # draw lines for whiskers - bottom, median, and top
+        for i, whisker in enumerate(
+                (quartiles[0], quartiles[2], quartiles[4])):
+            whisker_width = width if i == 1 else width / 2
+            shift = (width - whisker_width) / 2
+            xs = left_edge + shift
+            xe = left_edge + width - shift
+            self.svg.line(
+                parent_node,
+                coords=[(xs, self.view.y(whisker)),
+                        (xe, self.view.y(whisker))],
+                class_='reactive tooltip-trigger',
+                attrib={'stroke-width': 3})
+
+        # draw lines connecting whiskers to box (Q1 and Q3)
+        self.svg.line(
+            parent_node,
+            coords=[(left_edge + width / 2, self.view.y(quartiles[0])),
+                    (left_edge + width / 2, self.view.y(quartiles[1]))],
+            class_='reactive tooltip-trigger',
+            attrib={'stroke-width': 2})
+        self.svg.line(
+            parent_node,
+            coords=[(left_edge + width / 2, self.view.y(quartiles[4])),
+                    (left_edge + width / 2, self.view.y(quartiles[3]))],
+            class_='reactive tooltip-trigger',
+            attrib={'stroke-width': 2})
+
+        # 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,
+            class_='subtle-fill reactive tooltip-trigger')
+
+        return (left_edge + width / 2, self.view.y(
+            sum(quartiles) / len(quartiles)))
+
+    @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.
+
+        The iterator values may include None values.
+
+        Uses quartile definition from  Mendenhall, W. and
+        Sincich, T. L. Statistics for Engineering and the
+        Sciences, 4th ed. Prentice-Hall, 1995.
+        """
+        def median(seq):
+            n = len(seq)
+            if n % 2 == 0:  # seq has an even length
+                return (seq[n // 2] + seq[n // 2 - 1]) / 2
+            else:  # seq has an odd length
+                return seq[n // 2]
+
+        # sort the copy in case the originals must stay in original order
+        s = sorted([x for x in values if x is not None])
+        n = len(s)
+        if not n:
+            return 0, 0, 0, 0, 0
+        else:
+            q2 = median(s)
+            # See 'Method 3' in http://en.wikipedia.org/wiki/Quartile
+            if n % 2 == 0:  # even
+                q1 = median(s[:n // 2])
+                q3 = median(s[n // 2:])
+            else:  # odd
+                if n == 1:  # special case
+                    q1 = s[0]
+                    q3 = s[0]
+                elif n % 4 == 1:  # n is of form 4n + 1 where n >= 1
+                    m = (n - 1) // 4
+                    q1 = 0.25 * s[m-1] + 0.75 * s[m]
+                    q3 = 0.75 * s[3*m] + 0.25 * s[3*m + 1]
+                else:  # n is of form 4n + 3 where n >= 1
+                    m = (n - 3) // 4
+                    q1 = 0.75 * s[m] + 0.25 * s[m+1]
+                    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
+            return q0, q1, q2, q3, q4
diff --git a/pygal/graph/#pie.py# b/pygal/graph/#pie.py#
new file mode 100644
index 0000000..3e0826e
--- /dev/null
+++ b/pygal/graph/#pie.py#
@@ -0,0 +1,87 @@
+# -*- coding: utf-8 -*-
+# This file is part of pygal
+#
+# A python svg graph plotting library
+# Copyright © 2012-2014 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/>.
+"""
+Pie chart
+
+"""
+
+from __future__ import division
+from pygal.util import decorate
+from pygal.graph.graph import Graph
+from pygal.adapters import positive, none_to_zero
+from math import pi
+
+
+class Pie(Graph):
+    """Pie graph"""
+
+    _adapters = [positive, none_to_zero]
+
+    def slice(self, serie_node, start_angle, serie, total):
+        """Make a serie slice"""
+        dual = self._len > 1 and not self._order == 1
+
+        slices = self.svg.node(serie_node['plot'], class_="slices")
+        serie_angle = 0
+        total_perc = 0
+        original_start_angle = start_angle
+        center = ((self.width - self.margin.x) / 2.,
+                  (self.height - self.margin.y) / 2.)
+        radius = min(center)
+        for i, val in enumerate(serie.values):
+            perc = val / total
+            angle = 2 * pi * perc
+            serie_angle += angle
+            val = '{0:.2%}'.format(perc)
+            metadata = serie.metadata.get(i)
+            slice_ = decorate(
+                self.svg,
+                self.svg.node(slices, class_="slice"),
+                metadata)
+            if dual:
+                small_radius = radius * .9
+                big_radius = radius
+            else:
+                big_radius = radius * .9
+                small_radius = radius * self.config.inner_radius
+
+            self.svg.slice(
+                serie_node, slice_, big_radius, small_radius,
+                angle, start_angle, center, val)
+            start_angle += angle
+            total_perc += perc
+
+        if dual:
+            val = '{0:.2%}'.format(total_perc)
+            self.svg.slice(serie_node,
+                           self.svg.node(slices, class_="big_slice"),
+                           radius * .9, 0, serie_angle,
+                           original_start_angle, center, val)
+        return serie_angle
+
+    def _plot(self):
+        total = sum(map(sum, map(lambda x: x.values, self.series)))
+
+        if total == 0:
+            return
+        current_angle = 0
+        for index, serie in enumerate(self.series):
+            angle = self.slice(
+                self._serie(index), current_angle, serie, total)
+            current_angle += angle
diff --git a/pygal/graph/bar.py b/pygal/graph/bar.py
index a02c71d..879f272 100644
--- a/pygal/graph/bar.py
+++ b/pygal/graph/bar.py
@@ -23,7 +23,8 @@ Bar chart
 
 from __future__ import division
 from pygal.graph.graph import Graph
-from pygal.util import swap, ident, compute_scale, decorate
+from pygal.util import compute_scale, decorate
+from pygal.serie import NestedSerie
 
 
 class Bar(Graph):
@@ -36,8 +37,10 @@ class Bar(Graph):
         self._x_ranges = None
         super(Bar, self).__init__(*args, **kwargs)
 
-    def _bar(self, parent, x, y, index, i, zero, shift=True, secondary=False):
+    def _bar(self, parent, x, y, index, i, zero, errors_node, shift=True,
+             secondary=False, nested=None):
         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
@@ -54,12 +57,17 @@ class Bar(Graph):
             parent, 'rect',
             x=x, y=y, rx=r, ry=r, width=width, height=height,
             class_='rect reactive tooltip-trigger')
-        transpose = swap if self.horizontal else ident
-        return transpose((x + width / 2, y + height / 2))
+        transpose = self._transpose()
+        centers = transpose((x + width / 2, y + height / 2))
+        if nested:
+            error_coords = (self.view.y(nested.min), self.view.y(nested.max))
+            self._draw_error_marks(errors_node, x, error_coords, width, index)
+        return centers
 
     def bar(self, serie_node, serie, index, rescale=False):
         """Draw a bar graph for a serie"""
         bars = self.svg.node(serie_node['plot'], class_="bars")
+        errors_node = self.svg.node(serie_node['plot'], class_="errors_marks")
         if rescale and self.secondary_series:
             points = [
                 (x, self._scale_diff + (y - self._scale_min_2nd) * self._scale)
@@ -76,10 +84,12 @@ class Bar(Graph):
                 self.svg,
                 self.svg.node(bars, class_='bar'),
                 metadata)
-            val = self._format(serie.values[i])
-
+            val = self._get_value(points, i)
+            nested = serie.values[i] if isinstance(serie.values[i],
+                                                   NestedSerie) else None
             x_center, y_center = self._bar(
-                bar, x, y, index, i, self.zero, secondary=rescale)
+                bar, x, y, index, i, self.zero, errors_node,
+                secondary=rescale, nested=nested)
             self._tooltip_data(
                 bar, val, x_center, y_center, classes="centered")
             self._static_value(serie_node, val, x_center, y_center)
diff --git a/pygal/graph/base.py b/pygal/graph/base.py
index bf77066..778d1a4 100644
--- a/pygal/graph/base.py
+++ b/pygal/graph/base.py
@@ -1,4 +1,4 @@
- # -*- coding: utf-8 -*-
+# -*- coding: utf-8 -*-
 # This file is part of pygal
 #
 # A python svg graph plotting library
@@ -24,7 +24,8 @@ Base for pygal charts
 from __future__ import division
 from pygal.view import Margin, Box
 from pygal.util import (
-    get_text_box, get_texts_box, cut, rad, humanize, truncate, split_title)
+    get_text_box, get_texts_box, cut, rad, humanize, truncate,
+    split_title)
 from pygal.svg import Svg
 from pygal.util import cached_property
 from math import sin, cos, sqrt
@@ -203,25 +204,29 @@ class BaseGraph(object):
     def _secondary_min(self):
         """Getter for the minimum series value"""
         return (self.range[0] if (self.range and self.range[0] is not None)
-            else (min(self._secondary_values) if self._secondary_values else None))
+                else (min(serie.min for serie in self.secondary_series)
+                      if self._secondary_values else None))
 
     @cached_property
     def _min(self):
         """Getter for the minimum series value"""
-        return (self.range[0] if (self.range and self.range[0] is not None) 
-            else (min(self._values) if self._values else None))
+        return (self.range[0] if (self.range and self.range[0] is not None)
+                else (min(serie.min for serie in self.series)
+                      if self._values else None))
 
     @cached_property
     def _max(self):
         """Getter for the maximum series value"""
         return (self.range[1] if (self.range and self.range[1] is not None)
-            else (max(self._values) if self._values else None))
+                else (max(serie.max for serie in self.series)
+                      if self._values else None))
 
     @cached_property
     def _secondary_max(self):
         """Getter for the maximum series value"""
         return (self.range[1] if (self.range and self.range[1] is not None)
-            else (max(self._secondary_values) if self._secondary_values else None))
+                else (max(serie.max for serie in self.secondary_series)
+                      if self._secondary_values else None))
 
     @cached_property
     def _order(self):
@@ -245,6 +250,7 @@ class BaseGraph(object):
         return sum(
             map(len, map(lambda s: s.safe_values, self.series))) != 0 and (
             sum(map(abs, self._values)) != 0)
+        return any(map(lambda s: s.has_data, self.series))
 
     def render(self, is_unicode=False):
         """Render the graph, and return the svg string"""
diff --git a/pygal/graph/datey.py b/pygal/graph/datey.py
index bda6d6e..f218f00 100644
--- a/pygal/graph/datey.py
+++ b/pygal/graph/datey.py
@@ -40,6 +40,7 @@ from pygal._compat import total_seconds
 from pygal.adapters import date
 from pygal.util import compute_scale
 from pygal.graph.xy import XY
+from pygal.serie import NestedSerie
 import datetime
 
 
@@ -67,21 +68,25 @@ class DateY(XY):
         # Approximatively the same code as in XY.
         # The only difference is the transformation of dates to numbers
         # (beginning) and the reversed transformation to dates (end)
-        self._offset = min([val[0]
-                            for serie in self.series
-                            for val in serie.values
-                            if val[0] is not None]
-                           or [datetime.datetime.fromtimestamp(0)])
+        self._offset = min([s.min for s in self.series]
+                          or [datetime.datetime.fromtimestamp(0)])
+        # self._offset = min(
+        #     [val[0].min if isinstance(val[0], NestedSerie)
+        #      else val[0]
+        #      for serie in self.series
+        #      for val in serie._values
+        #      if val[0] is not None]
+        #     or [datetime.datetime.fromtimestamp(0)])
         for serie in self.all_series:
-            serie.values = [(self._tonumber(v[0]), v[1]) for v in serie.values]
+            serie._values = [(self._tonumber(v[0]), v[1]) for v in serie._values]
 
         xvals = [val[0]
                  for serie in self.series
-                 for val in serie.values
+                 for val in serie._values
                  if val[0] is not None]
         yvals = [val[1]
                  for serie in self.series
-                 for val in serie.values
+                 for val in serie._values
                  if val[1] is not None]
         if xvals:
             xmin = min(xvals)
diff --git a/pygal/graph/frenchmap.py b/pygal/graph/frenchmap.py
index 951c86d..f9202db 100644
--- a/pygal/graph/frenchmap.py
+++ b/pygal/graph/frenchmap.py
@@ -198,7 +198,7 @@ class FrenchMapDepartments(Graph):
         """Getter for series values (flattened)"""
         return [val[1]
                 for serie in self.series
-                for val in serie.values
+                for val in serie._values
                 if val[1] is not None]
 
     def _plot(self):
@@ -208,12 +208,12 @@ class FrenchMapDepartments(Graph):
 
         for i, serie in enumerate(self.series):
             safe_vals = list(filter(
-                lambda x: x is not None, cut(serie.values, 1)))
+                lambda x: x is not None, cut(serie._values, 1)))
             if not safe_vals:
                 continue
             min_ = min(safe_vals)
             max_ = max(safe_vals)
-            for j, (area_code, value) in enumerate(serie.values):
+            for j, (area_code, value) in enumerate(serie._values):
                 if isinstance(area_code, Number):
                     area_code = '%2d' % area_code
                 if value is None:
diff --git a/pygal/graph/graph.py b/pygal/graph/graph.py
index 3e025cc..8737915 100644
--- a/pygal/graph/graph.py
+++ b/pygal/graph/graph.py
@@ -24,9 +24,11 @@ Commmon graphing functions
 from __future__ import division
 from pygal.interpolate import INTERPOLATIONS
 from pygal.graph.base import BaseGraph
+from pygal.serie import NestedSerie
 from pygal.view import View, LogView, XYLogView
 from pygal.util import (
-    majorize, truncate, reverse_text_len, get_texts_box, cut, rad, decorate)
+    majorize, truncate, reverse_text_len, get_texts_box, cut, rad, decorate,
+    swap, ident)
 from math import sqrt, ceil, cos
 from itertools import repeat, chain
 
@@ -493,12 +495,13 @@ class Graph(BaseGraph):
 
     def _get_value(self, values, i):
         """Get the value formatted for tooltip"""
-        return self._format(values[i][1])
+        return self._format(values[i][1].mean if isinstance(
+            values[i][1], NestedSerie) else values[i][1])
 
     def _points(self, x_pos):
         for serie in self.all_series:
             serie.points = [
-                (x_pos[i], v)
+                (x_pos[i], v.mean if isinstance(v, NestedSerie) else v)
                 for i, v in enumerate(serie.values)]
             if serie.points and self.interpolate:
                 serie.interpolated = self._interpolate(x_pos, serie.values)
@@ -528,3 +531,12 @@ class Graph(BaseGraph):
 
     def _post_compute(self):
         pass
+
+    def _transpose(self):
+        return swap if self.horizontal else ident
+
+    def _draw_error_marks(self, node, x, error_coords, width, index):
+        """Draw error marks using std deviation."""
+        error_node = node
+        x = x + width / 2
+        self.svg.draw_errors(error_node, self._transpose(), x, error_coords)
diff --git a/pygal/graph/histogram.py b/pygal/graph/histogram.py
index 16c2f00..91ebcbc 100644
--- a/pygal/graph/histogram.py
+++ b/pygal/graph/histogram.py
@@ -37,7 +37,7 @@ class Histogram(Graph):
         """Getter for secondary series values (flattened)"""
         return [val[0]
                 for serie in self.series
-                for val in serie.values
+                for val in serie._values
                 if val[0] is not None]
 
     @cached_property
@@ -45,14 +45,14 @@ class Histogram(Graph):
         """Getter for secondary series values (flattened)"""
         return [val[0]
                 for serie in self.secondary_series
-                for val in serie.values
+                for val in serie._values
                 if val[0] is not None]
 
     @cached_property
     def xvals(self):
         return [val
                 for serie in self.all_series
-                for dval in serie.values
+                for dval in serie._values
                 for val in dval[1:3]
                 if val is not None]
 
@@ -60,7 +60,7 @@ class Histogram(Graph):
     def yvals(self):
         return [val[0]
                 for serie in self.series
-                for val in serie.values
+                for val in serie._values
                 if val[0] is not None]
 
     def _has_data(self):
@@ -92,7 +92,7 @@ class Histogram(Graph):
         bars = self.svg.node(serie_node['plot'], class_="histbars")
         points = serie.points
 
-        for i, (y, x0, x1) in enumerate(points):
+        for i, (y, x0, x1) in enumerate(serie._values):
             if None in (x0, x1, y) or (self.logarithmic and y <= 0):
                 continue
             metadata = serie.metadata.get(i)
@@ -101,7 +101,7 @@ class Histogram(Graph):
                 self.svg,
                 self.svg.node(bars, class_='histbar'),
                 metadata)
-            val = self._format(serie.values[i][0])
+            val = self._format(serie._values[i][0])
 
             x_center, y_center = self._bar(
                 bar, x0, x1, y, index, i, self.zero, secondary=rescale)
diff --git a/pygal/graph/line.py b/pygal/graph/line.py
index bf34ef6..f5b5889 100644
--- a/pygal/graph/line.py
+++ b/pygal/graph/line.py
@@ -22,6 +22,7 @@ Line chart
 """
 from __future__ import division
 from pygal.graph.graph import Graph
+from pygal.serie import NestedSerie
 from pygal.util import cached_property, compute_scale, decorate
 
 
@@ -121,6 +122,17 @@ class Line(Graph):
                 serie_node['plot'], view_values, close=self._self_close,
                 class_='line reactive' + (' nofill' if not self.fill else ''))
 
+        for i, (x, y) in enumerate(points):
+            x = self.view.x(x)
+            errors_node = self.svg.node(serie_node['overlay'],
+                                        class_="errors_marks")
+            nested = serie.values[i] if isinstance(serie.values[i],
+                                                   NestedSerie) else None
+            if nested:
+                error_coords = (self.view.y(nested.min),
+                                self.view.y(nested.max))
+                self._draw_error_marks(errors_node, x, error_coords, 0, i)
+
     def _compute(self):
         # X Labels
         x_pos = [
diff --git a/pygal/graph/stackedbar.py b/pygal/graph/stackedbar.py
index 8bd129c..442faad 100644
--- a/pygal/graph/stackedbar.py
+++ b/pygal/graph/stackedbar.py
@@ -90,7 +90,8 @@ class StackedBar(Bar):
             self._secondary_max = (positive_vals and max(
                 sum_(max(positive_vals)), self.zero)) or self.zero
 
-    def _bar(self, parent, x, y, index, i, zero, shift=False, secondary=False):
+    def _bar(self, parent, x, y, index, i, zero, errors_node, shift=False,
+             secondary=False, nested=None):
         if secondary:
             cumulation = (self.secondary_negative_cumulation
                           if y < self.zero else
@@ -124,4 +125,7 @@ class StackedBar(Bar):
             x=x, y=y, rx=r, ry=r, width=width, height=height,
             class_='rect reactive tooltip-trigger')
         transpose = swap if self.horizontal else ident
+        if nested:
+            error_coords = (self.view.y(nested.min), self.view.y(nested.max))
+            self._draw_error_marks(errors_node, x, error_coords, width, index)
         return transpose((x + width / 2, y + height / 2))
diff --git a/pygal/graph/supranationalworldmap.py b/pygal/graph/supranationalworldmap.py
index 4cc9a16..5bcf92d 100644
--- a/pygal/graph/supranationalworldmap.py
+++ b/pygal/graph/supranationalworldmap.py
@@ -43,13 +43,13 @@ class SupranationalWorldmap(Worldmap):
 
         for i, serie in enumerate(self.series):
             safe_vals = list(filter(
-                lambda x: x is not None, cut(serie.values, 1)))
+                lambda x: x is not None, cut(serie._values, 1)))
             if not safe_vals:
                 continue
             min_ = min(safe_vals)
             max_ = max(safe_vals)
-            serie.values = self.replace_supranationals(serie.values)
-            for j, (country_code, value) in enumerate(serie.values):
+            serie.values = self.replace_supranationals(serie._values)
+            for j, (country_code, value) in enumerate(serie._values):
                 if value is None:
                     continue
                 if max_ == min_:
diff --git a/pygal/graph/verticalpyramid.py b/pygal/graph/verticalpyramid.py
index 7c52ac9..cbd8f51 100644
--- a/pygal/graph/verticalpyramid.py
+++ b/pygal/graph/verticalpyramid.py
@@ -81,8 +81,9 @@ class VerticalPyramid(StackedBar):
                  y)
                 for y in y_pos]
 
-    def _bar(self, parent, x, y, index, i, zero, shift=True, secondary=False):
+    def _bar(self, parent, x, y, index, i, zero, errors_node, shift=True,
+             secondary=False, nested=None):
         if index % 2:
             y = -y
         return super(VerticalPyramid, self)._bar(
-            parent, x, y, index, i, zero, False, secondary)
+            parent, x, y, index, i, zero, False, secondary, nested)
diff --git a/pygal/graph/worldmap.py b/pygal/graph/worldmap.py
index 8e144d6..cc86eb3 100644
--- a/pygal/graph/worldmap.py
+++ b/pygal/graph/worldmap.py
@@ -44,7 +44,7 @@ class Worldmap(Graph):
     def countries(self):
         return [val[0]
                 for serie in self.all_series
-                for val in serie.values
+                for val in serie._values
                 if val[0] is not None]
 
     @cached_property
@@ -52,7 +52,7 @@ class Worldmap(Graph):
         """Getter for series values (flattened)"""
         return [val[1]
                 for serie in self.series
-                for val in serie.values
+                for val in serie._values
                 if val[1] is not None]
 
     def _plot(self):
@@ -62,12 +62,12 @@ class Worldmap(Graph):
 
         for i, serie in enumerate(self.series):
             safe_vals = list(filter(
-                lambda x: x is not None, cut(serie.values, 1)))
+                lambda x: x is not None, cut(serie._values, 1)))
             if not safe_vals:
                 continue
             min_ = min(safe_vals)
             max_ = max(safe_vals)
-            for j, (country_code, value) in enumerate(serie.values):
+            for j, (country_code, value) in enumerate(serie._values):
                 if value is None:
                     continue
                 if max_ == min_:
diff --git a/pygal/graph/xy.py b/pygal/graph/xy.py
index 24272ac..a6ea110 100644
--- a/pygal/graph/xy.py
+++ b/pygal/graph/xy.py
@@ -24,6 +24,7 @@ XY Line graph
 from __future__ import division
 from pygal.util import compute_scale, cached_property
 from pygal.graph.line import Line
+from pygal.serie import NestedSerie
 
 
 class XY(Line):
@@ -32,16 +33,16 @@ class XY(Line):
 
     @cached_property
     def xvals(self):
-        return [val[0]
+        return [val[0].mean if isinstance(val[0], NestedSerie) else val[0]
                 for serie in self.all_series
-                for val in serie.values
+                for val in serie._values
                 if val[0] is not None]
 
     @cached_property
     def yvals(self):
-        return [val[1]
+        return [val[1].mean if isinstance(val[1], NestedSerie) else val[1]
                 for serie in self.series
-                for val in serie.values
+                for val in serie._values
                 if val[1] is not None]
 
     def _has_data(self):
diff --git a/pygal/serie.py b/pygal/serie.py
index d3636b5..6b45b05 100644
--- a/pygal/serie.py
+++ b/pygal/serie.py
@@ -20,20 +20,95 @@
 Little helpers for series
 
 """
-from pygal.util import cached_property
+from pygal.util import cached_property, cut
+from math import fsum, sqrt
 
 
 class Serie(object):
     """Serie containing title, values and the graph serie index"""
-    def __init__(self, title, values, metadata=None):
+    def __init__(self, title, values, metadata=None, parent=None, dual=False):
         self.title = title
-        self.values = values
+        self._values = values
         self.metadata = metadata or {}
+        self.parent = parent
+        self.dual = dual
+
+
+    @cached_property
+    def values(self):
+        if self.dual:
+            return cut(self._values)
+        return self._values
 
     @cached_property
     def safe_values(self):
         return list(filter(lambda x: x is not None, self.values))
 
+    @cached_property
+    def min(self):
+        """Returns the lowest value of the serie."""
+        return min([val.min if isinstance(val, NestedSerie) else val
+                    for val in self.values if val is not None] or [None])
+
+    @cached_property
+    def max(self):
+        """Returns the lowest value of the serie."""
+        return max([val.max if isinstance(val, NestedSerie) else val
+                    for val in self.values if val is not None] or [None])
+
+    @cached_property
+    def length(self):
+        """Returns the serie size."""
+        return len(self.values)
+
+    @cached_property
+    def has_data(self):
+        """True if data is provided."""
+        datalen = len(self.safe_values)
+        total = 0
+        for v in self.safe_values:
+            if v:
+                if isinstance(v, NestedSerie):
+                    total += v.abs
+                elif isinstance(v, tuple):
+                    total += any([abs(v[0] or 0) != 0, abs(v[1] or 0) != 0])
+                else:
+                    total += abs(v)
+        return datalen and total != 0
+
+
+class NestedSerie(Serie):
+    """Class that handles nested series."""
+    @cached_property
+    def mean(self):
+        """Returns the average on the serie (mean)."""
+        return fsum([v for v in self.values]) / self.length
+
+    @cached_property
+    def variance(self):
+        """Returns the variance for the serie."""
+        return 1/self.length * fsum((v-self.mean) ** 2 for v in self.values)
+
+    @cached_property
+    def deviation(self):
+        """Returns the deviation for the serie."""
+        return sqrt(self.variance)
+
+    @cached_property
+    def min(self):
+        """Returns the lowest value of the serie."""
+        return self.mean - self.deviation
+
+    @cached_property
+    def max(self):
+        """Returns the lowest value of the serie."""
+        return self.mean + self.deviation
+
+    @cached_property
+    def abs(self):
+        """Returns the absolute value of the serie."""
+        return abs(self.mean)
+
 
 class Label(object):
     """A label with his position"""
diff --git a/pygal/svg.py b/pygal/svg.py
index 76956fe..f1f872e 100644
--- a/pygal/svg.py
+++ b/pygal/svg.py
@@ -235,3 +235,32 @@ class Svg(object):
         if self.graph.disable_xml_declaration or is_unicode:
             svg = svg.decode('utf-8')
         return svg
+
+    def draw_errors(self, parent_node, transpose, x, y_coords):
+        """Draws the chart errors aka confidence level."""
+        width = (
+            self.graph.view.x(1) - self.graph.view.x(0)) / self.graph._len
+        series_margin = width * getattr(self.graph, '_series_margin', 1)
+        width -= 2 * series_margin
+        y_begin = y_coords[0]
+        y_end = y_coords[1]
+        line_edges = transpose((x, y_begin)), transpose((x, y_end))
+        line_feet = (transpose((x - width / 4, y_begin)),
+                     transpose((x + width / 4, y_begin)))
+        line_hat = (transpose((x - width / 4, y_end)),
+                    transpose((x + width / 4, y_end)))
+        self.line(
+            parent_node,
+            coords=[line_edges[0], line_edges[1]],
+            class_='errors'
+        )
+        self.line(
+            parent_node,
+            coords=[line_feet[0], line_feet[1]],
+            class_='errors'
+        )
+        self.line(
+            parent_node,
+            coords=[line_hat[0], line_hat[1]],
+            class_='errors'
+        )
diff --git a/pygal/util.py b/pygal/util.py
index a0608a9..c33308a 100644
--- a/pygal/util.py
+++ b/pygal/util.py
@@ -318,7 +318,7 @@ def safe_enumerate(iterable):
         if v is not None:
             yield i, v
 
-from pygal.serie import Serie
+from pygal.serie import Serie, NestedSerie
 
 
 def prepare_values(raw, config, cls):
@@ -376,6 +376,12 @@ def prepare_values(raw, config, cls):
                 raw_value = dict(raw_value)
                 value = raw_value.pop('value', None)
                 metadata[index] = raw_value
+            elif is_list_like(raw_value) and not cls._dual:
+                value = NestedSerie(title, raw_value, metadata)
+            elif (is_list_like(raw_value) and cls._dual and
+                  len(raw_value) > 1 and is_list_like(raw_value[1])):
+                value = (raw_value[0],
+                         NestedSerie(title, raw_value[1], metadata))
             else:
                 value = raw_value
 
@@ -399,7 +405,11 @@ def prepare_values(raw, config, cls):
             else:
                 value = adapter(value)
             values.append(value)
-        series.append(Serie(title, values, metadata))
+        serie = Serie(title, values, metadata, dual=cls._dual)
+        for v in serie.values:
+            if isinstance(v, NestedSerie):
+                v.parent = serie
+        series.append(serie)
     return series