Sorting Based on "Deep" Metricsedit
In the prior examples, the metric was a direct child of the bucket. An average price was calculated for each term. It is possible to sort on deeper metrics, which are grandchildren or greatgrandchildren of the bucket—with some limitations.
You can define a path to a deeper, nested metric by using angle brackets (>
), like
so: my_bucket>another_bucket>metric
.
The caveat is that each nested bucket in the path must be a singlevalue bucket.
A filter
bucket produces a single bucket: all documents that match the
filtering criteria. Multivalue buckets (such as terms
) generate many
dynamic buckets, which makes it impossible to specify a deterministic path.
Currently, there are only three singlevalue buckets: filter
, global
, and reverse_nested
. As
a quick example, let’s build a histogram of car prices, but order the buckets
by the variance in price of red and green (but not blue) cars in each price range:
GET /cars/transactions/_search { "size" : 0, "aggs" : { "colors" : { "histogram" : { "field" : "price", "interval": 20000, "order": { "red_green_cars>stats.variance" : "asc" } }, "aggs": { "red_green_cars": { "filter": { "terms": {"color": ["red", "green"]}}, "aggs": { "stats": {"extended_stats": {"field" : "price"}} } } } } } }
Sort the buckets generated by the histogram according to the variance of a nested metric. 

Because we are using a singlevalue 

Sort on the stats generated by this metric. 
In this example, you can see that we are accessing a nested metric. The stats
metric is a child of red_green_cars
, which is in turn a child of colors
. To
sort on that metric, we define the path as red_green_cars>stats.variance
.
This is allowed because the filter
bucket is a singlevalue bucket.