Clarify the docs for numeric_histogram
From the description of numeric_histogram, it was unclear what the
keys and values of the returned map were.  This clarifies that
the keys are the centers of the bin, and the entries are the
counts/total weights of the bin.
@@ -277,8 +277,9 @@ Approximate Aggregate Functions
.. function:: numeric_histogram(buckets, value, weight) -> map<double, double>
Computes an approximate histogram with up to ``buckets`` number of buckets
- for all ``value``\ s with a per-item weight of ``weight``. The algorithm
- is based loosely on:
+ for all ``value``\ s with a per-item weight of ``weight``. The keys of the
+ returned map are roughly the center of the bin, and the entry is the total
+ weight of the bin. The algorithm is based loosely on:
.. code-block:: none
@@ -292,6 +293,7 @@ Approximate Aggregate Functions
Computes an approximate histogram with up to ``buckets`` number of buckets
for all ``value``\ s. This function is equivalent to the variant of
:func:`numeric_histogram` that takes a ``weight``, with a per-item weight of ``1``.
+ In this case, the total weight in the returned map is the count of items in the bin.
Statistical Aggregate Functions
-------------------------------
