Configuring Expressions in Amazon CloudSearch
You can define numeric expressions and use them to sort search results. Expressions can also be returned in search results. You can add expressions to the domain configuration or define expressions within search requests.
Topics
Writing Expressions for Amazon CloudSearch
Amazon CloudSearch expressions can contain:

Single value, sort enabled numeric fields (
int
,double
,date
). (You must specify a specific field, wildcards are not supported.) 
Other expressions

The
_score
variable, which references a document's relevance score 
The
_time
variable, which references the current epoch time 
The
_rand
variable, which returns a randomly generated value 
Integer, floating point, hex, and octal literals

Arithmetic operators:
+  * / %

Bitwise operators:
 & ^ ~ << >> >>>

Boolean operators (including the ternary operator):
&&  ! ?:

Comparison operators:
< <= == >= >

Mathematical functions:
abs ceil exp floor ln log10 logn max min pow sqrt

Trigonometric functions:
acos acosh asin asinh atan atan2 atanh cos cosh sin sinh tanh tan

The
haversin
distance function
JavaScript order of precedence rules apply for operators. You can override operator precedence by using parentheses.
Shortcut evaluation is used when evaluating logical expressions—if the value of the
expression can be determined after evaluating the first argument, the second argument
is not
evaluated. For example, in the expression a  b
, b
is only
evaluated if a
is not true.
Expressions always return an integer value from 0 to the maximum 64bit signed integer value (2^63  1). Intermediate results are calculated as doubleprecision floating point values and the return value is rounded to the nearest integer. If the expression is invalid or evaluates to a negative value, it returns 0. If the expression evaluates to a value greater than the maximum, it returns the maximum value.
Expression names must begin with a letter and be at least 3 and no more than 64 characters long. The following characters are allowed: az (lowercase letters), 09, and _ (underscore). The name score is reserved and cannot be used as an expression name.
For example, if you define an int
field named popularity for your
domain, you could use that field in conjunction with the default relevance _score
to
construct a custom expression.
(0.3*popularity)+(0.7*_score)
Note that this simple example assumes that the popularity ranking and the relevance _score values are in about the same range. To tune your expressions for ranking results, you need to do some testing to determine how to weight the components of your expressions to get the results you want.
Using Date Fields in Amazon CloudSearch Expressions
The value from a date
field is stored as an epoch time with millisecond resolution. This means you can
use the mathematical and comparison operators to construct expressions using dates
stored in your documents and the current epoch time (_time
). For example, using the following expression to sort search results from the movies
domain pushes movies with recent release dates toward the top of the list.
_score/(_time  release_date)