Initial grouped bars, issue with scale. wireservice#26

leather/chart.py

@@ -156,6 +156,20 @@ def add_lines(self, data, x=None, y=None, name=None, color=None, width=None):
 
         self.add_series(Series(data, Lines(color, width), x=x, y=y, name=name))
 
+    def add_grouped_bars(self, data, x=None, y=None, name=None, color=None):
+        """
+        Create and add multiple :class:`.Series` rendered with :class:`.Bars`.
+        
+        Data should be a sequence of :class:`.Series` data, one for each bar in
+        a group.
+
+        Color should be a sequence of colors, one for each bar in a group.
+        """
+        if not color:
+            color = self._series_colors.pop(0)
+
+        self.add_series(Series(data, Bars(color, grouped=True), x=x, y=y, name=name))
+
     def _validate_dimension(self, dimension):
         """
         Validates that the given scale and axis are valid for the data that

leather/shapes/bars.py

@@ -5,6 +5,7 @@
 import six
 
 from leather.shapes.base import Shape
+from leather.utils import Y
 
 
 class Bars(Shape):
@@ -14,9 +15,13 @@ class Bars(Shape):
     :param color:
         The color to fill the bars. You may also specify a
         :func:`.style_function`.
+    :param grouped:
+        If True, any values in data with equal x values will be rendered as
+        grouped bars. Defaults to False.
     """
-    def __init__(self, fill_color):
+    def __init__(self, fill_color, grouped=False):
         self._fill_color = fill_color
+        self._grouped = grouped
 
     def to_svg(self, width, height, x_scale, y_scale, series):
         """
@@ -27,11 +32,25 @@ def to_svg(self, width, height, x_scale, y_scale, series):
 
         zero_x = x_scale.project(0, 0, width)
 
+        if self._grouped:
+            y_values = series.values(Y)
+            y_counts = {y: y_values.count(y) for y in set(y_values)}
+
+            seen_y_counts = {y: 0 for y in set(y_values)}
+
         for i, (x, y, row) in enumerate(series):
             if x is None or y is None:
                 continue
 
             y1, y2 = y_scale.project_interval(y, height, 0)
+
+            if self._grouped:
+                group_height = (y1 - y2) / y_counts[y]
+
+                y1 = y2 + (group_height * (seen_y_counts[y] + 1))
+                y2 = y2 + (group_height * seen_y_counts[y])
+                seen_y_counts[y] += 1
+
             proj_x = x_scale.project(x, 0, width)
 
             if x < 0: