Facets are used for grouping documents based on some criteria, for example specific terms or a date range.
Range facets group documents based on ranges into which a numeric or `DateTime` field falls. Unlike [Histogram facets](🔗), the ranges need not be an interval, such as 0-10, 10-20. Instead, they can be different sizes and overlap each other, such as 0-10, 5-20. Also unlike histogram facets, range facets return more than just the number of documents in each range, such as minimum, maximum, and mean values.
To request range facets, use the `RangeFacetFor` method. Its first parameter is an expression, which you use to select the property by which to group documents. The second parameter is an array (params) of either `NumericRange` or `DateRange` objects, depending on the first parameter's property type. Both numeric or `DateTime` field range types have two properties, named From and To, of type nullable double and nullable `DateTime`, respectively.
After executing a search request with range facets, you retrieve facets from the result object using the `RangeFacetFor` method (the same name used to request them). This method has one parameter, an expression saying what property the range facet is for.
Note
Ranges are inclusive for the lower bound and exclusive for the upper bound. That is, a range from 0 to 10 matches 0 but not 10. The same goes for date ranges, where a range from 2012-01-01 to 2012-01-31 matches 2012-01-01 but not 2012-01-31.
The following example groups products into three price ranges.
In the above example, you create a number of ranges and request a range facet for products falling into those ranges. In the first range, you do not specify the From property, effectively saying that the range is for products with a price below 100. Similarly, the third range does not specify the To property, requesting all products that cost 300 or more.
Upon retrieving the search result, you can retrieve and inspect the facet. Below is an example of doing this, writing information about each range to the console.
The above code produces output like this:
Range to 100 Count: 61 Min: 0,5 Max: 97,3 Mean: 42,3237045467812 Total: 2581,74597735365
Range from 100 to 300 Count: 52 Min: 100,0 Max: 299,0 Mean: 205,738167025743 Total: 10698,3846853387
Range from 300 Count: 51 Min: 301,5 Max: 942,8 Mean: 566,562194859469 Total: 28894,6719378329