Hammering on aggregation.

docs/views_bundles.rst

@@ -1,3 +1,46 @@
 ===========================================
 Aggregating datasets with Views and Bundles
 ===========================================
+Just as Treants and Trees have the :class:`~datreant.data.limbs.Data` limb 
+for storing and retrieving datasets in their filesystem trees, the
+:class:`~datreant.core.View` and :class:`~datreant.core.Bundle` objects also
+have the :class:`~datreant.data.agglimbs.AggData` limb for accessing these
+datasets in aggregate.
+
+Given a directory with four Treants ::
+
+    > ls
+    elm/  maple/  oak/  sequoia/
+
+we'll gather these up in a Bundle ::
+
+    >>> import datreant.core as dtr
+    >>> import glob
+    >>> b = dtr.Bundle(glob.glob('*'))
+    >>> b
+    <Bundle([<Treant: 'sequoia'>, <Treant: 'maple'>, <Treant: 'oak'>, <Treant: 'elm'>])>
+
+and then attach the :class:`~datreant.data.limbs.AggData` limb to only this
+Bundle instance with::
+
+    >>> import datreant.data
+    >>> b.attach('data')
+
+.. note:: Attaching a limb like :class:`~datreant.data.agglimbs.AggData` to a
+          Bundle or View with the :meth:`~datreant.core.Bundle.attach` method
+          will attach the required limb to each member instance. In this case,
+          each member gets a :class:`~datreant.data.limbs.Data` limb.
+
+and so we can now do::
+
+    >>> b.data
+    <AggData([])>
+
+This tells us that there are no datasets with the same key within every member
+of the Bundle. So, let's make something that does. Let's build a "dataset" that
+gives us a sinusoid based on a characteristic of each Treant in the Bundle::
+
+    >>> b.categories['amplitude'] = [1, 2, 3, 4]
+    >>> for member in b:
+    ...    member.data
+