Filtering and Boosting

Filtering

In filtering, the expression must return boolean value for each item. If the returned value is true, the item passed the filter; if the value is false, the item does not pass and will be discarded. The value is computed from set property values of the individual items.

Consider the following table of items in sample movie-recommendation domain:

Name: string	Year:int	Director: string		Genres: set	Parental-Advisory:boolean
Pulp Fiction	1994	Quentin Tarantino		{“Crime Fiction”,”Drama” “Thriller” }	true
King Kong	2005	Peter Jackson		{“Action”, “Drama”, “Adventure” }	false
Fight Club	1999	David Fincher		{“Drama”, “Existentialism”}	true
The Lord of the Rings: The Return of the King	2003	Peter Jackson		{ “Adventure”, “Fantasy”, “Action” }	false
The Dark Knight	2008	Christopher Nolan		{“Superhero”,”Drama” ,”Action”,”Adventure”, “Thriller”,”Crime Fiction”}	false
Silence of the Lambs	1991	Jonathan Demme		{“Crime Fiction”, “Drama”, “Thriller”, “Horror” }	true
Dead Alive	1992	Peter Jackson		{“Horror”, “Comedy”}	true
… and 10000 other movies

Example 1

By default, when items are to be recommended to a given user, the recommender selects any items which seem relevant to the user. However, it may be your policy not to recommend items with Parental-Advisory flag set on. Hence you may use the following simple ReQL filtering expression:

not 'Parental-Advisory'

Then the recommender may only choose from the following movies:

Name: string	Year:int	Director: string		Genres: set	Parental-Advisory:boolean
King Kong	2005	Peter Jackson		{“Action”, “Drama”, “Adventure” }	false
The Lord of the Rings: The Return of the King	2003	Peter Jackson		{ “Adventure”, “Fantasy”, “Action” }	false
The Dark Knight	2008	Christopher Nolan		{“Superhero”,”Drama” ,”Action”,”Adventure”, “Thriller”,”Crime Fiction”}	false
… and 5926 other movies

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Example 2

If you want to allow only items without Parental-Advisory which were directed by Peter Jackson (for example because a user selected such a filter at your site) you can do it by:

(not 'Parental-Advisory') and ('Director' == "Peter Jackson")

Note

You can access value of a property by putting name of the property into the single quotes. Strings are enclosed in double quotes.

Only following items can be recommended:

Name: string	Year:int	Director: string	Genres: set	Parental-Advisory:boolean
King Kong	2005	Peter Jackson	{“Action”, “Drama”, “Adventure” }	false
The Lord of the Rings: The Return of the King	2003	Peter Jackson	{ “Adventure”, “Fantasy”, “Action” }	false

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Example 3

As another example, consider that user entered the Thriller section of your system’s catalog. Then you sure wish to recommend thrillers, ignoring the fact that usually, the user likes comedies.

As the Genres is a set property, you can use the in operator for checking whether Thriller is listed in the item’s genres:

"Thriller" in 'Genres'

Only the following items pass the filter:

Name: string	Year:int	Director: string		Genres: set	Parental-Advisory:boolean
Pulp Fiction	1994	Quentin Tarantino		{“Crime Fiction”,”Drama” “Thriller” }	true
The Dark Knight	2008	Christopher Nolan		{“Superhero”,”Drama” ,”Action”,”Adventure”, “Thriller”,”Crime Fiction”}	false
Silence of the Lambs	1991	Jonathan Demme		{“Crime Fiction”, “Drama”, “Thriller”, “Horror” }	true
… and 3141 other movies

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Handling deleted items

Filtering offers you an elegant way of handling deleted/obsolete items in the catalog. In many situations, it may happen that some items become unavailable and hence should not be recommended anymore. Considering interaction data, however, such items may still be important for the recommender. For example, the recommender may find out that users who liked a no more available item, x, will probably like another item, y, which is still available. Therefore, it is undesirable to simply delete x, deleting also all the related interactions in cascade.

With filtering, you may handle item deletes using the following scheme:

• Create a dedicated item property, such as deleted, of type boolean (the implicit value for all items will be null, which is OK).

• For deleted items, set the value of deleted true.

• For recommendations, use the following filter:

not 'deleted'

• If the item becomes available again, you may set deleted to false.

Such a mechanism cay easily be extended to control availability over different regions, customer licenses, etc.

Boosting

In advanced applications, besides filtering, you may wish to boost recommendation rates of some items. In contrast to filtering, where items may be completely blocked, in boosting, you may tell the recommender to prefer some items among others. Indeed, by default, it is a task of the recommender itself to select the items which are the most relevant. However, it may be your policy to purposefully bias the recommender toward your business goals.

For example, considering the above table of movies, one may wish to promote the movies which are new and were filmed after 2000, especially if they were filmed after 2005. Then the following boosting query can handle that:

if 'Year' <= 2000 then 1 else (if 'Year' <= 2005 then 1.5 else 2)

As you can see, boosting expressions return numbers rather than booleans as in case of filtering. Specifically, they provide the items with coefficients by which the internal scores determined by the recommender will be multiplied.

The boosting coefficients assigned by the query are shown in the following table:

Name: string	Year:int	Boosting
Pulp Fiction	1994	1.0
King Kong	2005	1.5
Fight Club	1999	1.0
The Lord of the Rings: The Return of the King	2003	1.5
The Dark Knight	2008	2.0
Silence of the Lambs	1991	1.0
Dead Alive	1992	1.0
… and 10000 other movies

Examples

Exclude some items from recommendations using their IDs

Use filter:

'itemId' not in {"item-127", "item-756", "item-568"}

The three items will not be recommended.

Recommend related items by the same manufacturer

Suppose that the items have a string property manufacturer and the user is viewing a product detail page.

If you want to give the user related items using Recommend Items to Item, but restrict them to the manufacturer of the currently viewed item, use filter:

'manufacturer' == context_item["manufacturer"]

context_item function is used for retrieving property values of the item, that is currently viewed by the user.

Boost items that were published in last 24 hours

Suppose that the items have a timestamp property published_date. Then you can use this booster:

if 'published_date' >= now() - 24 * 60 * 60 then 2 else 1

now returns current UTC timestamp in seconds.

24 * 60 * 60 is the number of seconds in 24 hours.

Up-sell

Suppose that the items have a double property price. Slightly boost items that are more expensive then the currently viewed one with following booster in Recommend Items to Item:

if 'price' > context_item["price"] then 1.2 else 1

Recommend only items available in user’s city

• Suppose that the items have a set property cities. It contains cities in which the items are available.

• Suppose that the users have a string property city giving the city where each user live.

To recommend only items available in a user’s city, use filter:

context_user["city"] in 'cities'

context_user function is used for retrieving property values of the user for which you request the recommendations.

Recommend only items from subscribed topics

Assume your site contains articles about various topics. The users can choose which topics are interesting for them in order to receive personalized newsletters with articles from these topics.

• The subscribed topics are stored for each user in a User property of type set called subscribed_topics.

• Each article can belong to multiple topics, stored in the topics item property of the type set.

The following filter allows only items that contain at least one matching topic to be recommended:

size(context_user["subscribed_topics"] & 'topics') > 0

The & operator returns the intersection of the two sets, which must be non-empty.

Value Types and Operators

ReQL support following value types:

• int – signed integer (currently 64bit),

• double – double-precision floating-point number (IEEE 754 compliant),

• timestamp – UTC timestamp, similar to double,

• string – sequence of Unicode characters,

• boolean – binary data type of two possible values: true or false,

• set – unordered collection of values.

• array – ordered collection of values.

Except for set and aray types, all of the types include special value of null, which, again, corresponds to the fact that null is an allowed and also default value for the item / user property values in the API.

Numbers

Notation

Expression	Equivalent	Comment
0123.000	123.0	Leading and trailing zeros are ignored.
1.23e+3	1230.0	Exponential notation may be used.
1e9	1000000000	Using simple exponential notation for huge numbers.
123E-2	1.23	Negative exponents may also be used. Case of the e character does not matter.

Operations

Expression	Result	Comment
1 + 2	3	Addition.
1 + 2 + 3 + 4	10	Chain of additions.
1 - 2	-1	Subtraction.
1 - 2 - 3 - 4	-9	Chain of subtractions.
-(1 + 2)	-3	Unary minus.
2 * 3	6	Multiplication.
1 + 2 * 3 - 4	3	Standard operator precedence.
(1 + 2) * (3 - (4 + 5))	-18	Bracketing.
10 / 5	2.0	Division.
1 / 2	0.5	Division always results in double, event if the operands are integers!
5 / 0	NaN	If the divisor is 0, the result is NaN.
9 % 4	1	Modulo division.
3.14 % 2.5	0.64	Modulo division also works for doubles.
5 % 0	NaN	If the divisor is 0, the result is NaN.

Comparison

Expression	Result	Comment
1 < 2.0	true	Integers, doubles, and timestamps may be compared using standard comparison operators.
1 < 2 <= 2 == 2 != 1 >= 1 > 0	true	Comparison operators may be arbitrarily chained.
1 < 2 <= 2 == 3 != 1 >= 1 > 0	false	Chain of comparisons returns true if and only if all the individual comparisons are true.
2 == 2.0	true	In comparison, there is no difference between integers, doubles, and timestamps.

Strings

Notation

Expression	Comment
"foo"	Strings constants are enclosed in double quotes.
""	Empty string.
"she said \"hello\""	Double quotes must be escaped.
"she said 'hello'"	Single quotes needn’t be escaped.

Comparison

Expression	Result	Comment
"foo" == "foo"	true	Strings are compared for equality with ==.
"Alice" != null	true	Strings can be compared to null.
"Alice" < "Bob"	true	Strings are ordered in lexicographic order
"Alice" < "Bob" < "Carol" < "Dan"	true	Comparisons may be chained arbitrarily.
"Alice" < "Bob" <= "Carol" != "Dan"	true	Comparisons in the chain may be of different types.
"Alice" < "Bob" >= "Carol" != "Dan"	false	All the comparisons must hold for the chain to return true.
"Alice" < 5	error	Strings are only comparable with strings.
"Alice" ~ "A[a-z]+"	true	Strings can be matched with regular expressions (regex).

Containment

Expression	Result	Comment
"ice" in "Alice"	true	in operator between strings tests whether the first string is contained in the second string.
"Ice" in "Alice"	false	Containment test is case sensitive.
"ice" not in "Alice"	false	in operator may be negated for better readability.
"" in "abc"	true	Empty string is contained in every string.
"abc" in ""	false	No non-empty string is contained in empty string.
5 in "abc"	error	Both operands must be strings for string containment testing.

Concatenation

Expression	Result	Comment
"foo" + "bar"	"foobar"	Strings can be concatenated using the + operator.
"" + "foo" + ""	"foo"	Empty string is neutral element for concatenation.
"foo" + 123	"foo123"	Strings can be concatenated with integers.
"foo" + 123.0	"foo123.0"	Strings can be concatenated with numbers.

Indexing and Slicing

Expression	Result	Comment
"abcd"[1]	"b"	A character in the string can be accessed by its index (starting from 0).
"abcd"[10]	""	Requesting an index outside the array boundaries results in an empty string.
"abcd"[-1]	"d"	Negative indices are interpreted as counting from the end of the string. -1 therefore means the last character.
"abcd"[1:3]	"bc"	It is possible to get a sub-string between two indices
"abcd"[1:]	"bcd"	If the second index is omitted, all characters until the end of the string are returned.

Sets

Notation

Expression	Comment
{}	Empty set.
{1, 2, 3}	Set containing three integers.
{1, 2.0, false, "foo", null}	Sets may contain values of different types. This is an extension to sets in the API, which may only contain strings.
{{1,2}, {2,3}}	Sets may be nested.

Properties

Expression	Result	Comment
{ 1, 1, 1, 2 }	{ 1, 2 }	Sets only contain unique elements.
{ 1, 1.0 }	{ 1.0 }	Integers, doubles, and timestamps, are merged.
{ {1,2}, {2,1} }	{ {1,2} }	Merging also works for nested sets.

Value Containment

Expression	Result	Comment
2 in { 1, 2, 3 }	true	Using in operator, you may test whether a value is contained in given set (the ∈ relation)
4 not in { 1, 2, 3 }	true	The in operator may be negated for better readability (the ∉ relation).
2.0 in { 1, 2, 3 }	true	There is no difference between integers, doubles, and timestamps when testing containment.
"2" in { 1, 2, 3 }	false	There is a difference between numbers and strings.
{ 1, 2 } in { 1, 2, 3 }	false	in stays for ∈, not ⊆!
{ 1, 2 } in { {1,2}, {3,4} }	true	in stays for ∈.

Comparison

Expression	Result	Comment
{ 1, 2 } < { 1, 2, 3 }	true	Using < operator, you may test whether one test is a proper subset of another set (⊂ operator in set algebra).
{ 1, 2 } < { 1, 2 }	false	No set is a proper subset of itself.
{} < { 1, 2 }	true	Empty set is a proper subset of every non-empty set.
{} < {}	false	Empty set is not a proper subset of itself.
{ 1, 2 } <= { 1, 2, 3 }	true	Using <= operator, you may test whether one set is a subset of another set (⊆ operator is set algebra).
{ 1, 2 } <= { 1, 2 }	true	Every set is a subset of itself.
{ 1, 2 } == { 1, 2 }	true	== tests whether two sets are identical.
{ 1, 2 } != { 1, 2 }	false	!= tests whether two sets are different.
{ 1, 2, 3 } >= { 1, 2 }	true	>= operator tests whether one set is a superset of another set (⊇ operator in set algebra).
{ 1, 2 } >= { 1, 2 }	true	Every set is a superset of itself.
{ 1, 2, 3 } > { 1, 2 }	true	> operator tests whether one set is a proper superset of another set (⊃ operator in set algebra).
{ 1, 2 } > { 1, 2 }	false	A non-empty set in not a proper superset of itself.
{ 1, 2 } > {}	true	Every non-empty set is a proper superset of an empty set.
{} > {}	false	Empty set is not a proper subset of itself.

Union

Expression	Result	Comment
{ 1, 2 } + { 2, 3 }	{ 1, 2, 3 }	Sets may be unified using the + operator (∪ in set algebra).
{ 1, 2.0 } + { 2, 3 }	{ 1, 2.0, 3 }	Integers, doubles, and timestamps are merged when unifying sets.
{ 1, 2 } + { 2, 3 } + { 4 }	{ 1, 2, 3, 4 }	Unions may be chained.
{ 1, 2 } + {}	{ 1, 2 }	Unification with empty set has no effect on the original set.
{ 1, 2 } + { "2", "3" }	{ 1, 2, "2", "3" }	Strings and numbers are handled as different values.

Difference

Expression	Result	Comment
{ 1, 2 } - { 2, 3 }	{ 1 }	Set difference may be obtained using the - operator (operator is set algebra).
{ 1, 2 } - { 2.0, 3.0 }	{ 1 }	Integers, doubles, and timestamps are considered equal if they equal in values.
{ 1, 2 } - {}	{ 1, 2 }	Subtracting an empty set has no effect.
{ 1, 2 } - { 1 } - { 2 }	{}	Chaining of set subtractions works from left to rights.
{ 1, 2 } - ({ 1, 2 } - { 2 })	{ 2 }	Parenthesizing also works.

Intersection

Expression	Result	Comment
{ 1, 2 } & { 2, 3 }	{ 2 }	Set intersection may be obtained using the & operator.
{ 1, 2 } & { 2.0, 3.0 }	{ 2 }	Integers, doubles, and timestamps are considered equal if they equal in values.
{ 1, 2 } & {"1", "2"}	{}	Strings and numbers are handled as different values.
{"a", { 1, 2 }} & {"b", { 1, 2 }}	{{1,2}}	Works with subsets.

Symmetric difference

Expression	Result	Comment
{ 1, 2 } / { 2, 3 }	{ 1, 3 }	Symmetric difference of sets may be obtained using the / operator.
{ 1, 2 } / { 2.0, 3.0 }	{ 1, 3 }	Integers, doubles, and timestamps are considered equal if they equal in values.
{ 1, 2 } / {"1", "2"}	{1, 2, "1", "2"}	Strings and numbers are handled as different values.
{"a", { 1, 2 }} / {"b", { 1, 2 }}	{"a", "b"}	Works with subsets.

Arrays

Notation

Expression	Comment
[]	Empty array.
[1, 2, 3]	Array containing three integers.
[1, 2.0, false, "foo", null]	Arrays may contain values of different types.
[[1,2], [2,3]]	Arrays may be nested.

Value Containment

Expression	Result	Comment
2 in [ 1, 2, 3 ]	true	Using the in operator, you may test whether a value is contained in a given array.
4 not in [ 1, 2, 3 ]	true	The in operator may be negated for better readability.
2.0 in [ 1, 2, 3 ]	true	There is no difference between integers, doubles, and timestamps when testing containment.
"2" in [ 1, 2, 3 ]	false	There is a difference between numbers and strings.

Comparison

Expression	Result	Comment
[ 1, 2 ] == [ 1, 2 ]	true	== tests whether two arrays are identical.
[ 1, 2 ] != [ 1, 2 ]	false	!= tests whether two arrays are different.
[ 1, 2 ] != [ 2, 1 ]	true	Order of the elements must be the same in both arrays for equality

Concatenation

Expression	Result	Comment
[ 1, 2 ] + [ 3, 4 ]	[ 1, 2, 3, 4 ]	Arrays may be concatenated using the + operator.
[ 1 ] + [ 2, 3 ] + [ 4 ]	[ 1, 2, 3, 4 ]	Concatenations may be chained.
[ 1, 2 ] + []	[ 1, 2 ]	Concatenating an empty array has no effect on the original array.

Indexing and Slicing

Expression	Result	Comment
[ "a", "b", "c", "d" ][1]	"b"	Value can be accessed by their index (starting from 0).
[ "a", "b", "c", "d" ][10]	null	Requesting an index outside the array boundaries results in null.
[ "a", "b", "c", "d" ][-1]	"d"	Negative indices are interpreted as counting from the end of the array. -1 therefore means the last element.
[ "a", "b", "c", "d" ][1:3]	["b", "c"]	It is possible to get a sub-array between two indices
[ "a", "b", "c", "d" ][1:]	["b", "c", "d"]	If the second index is omitted, all elements until the end of the array are returned.

Logical Operators

Negation (NOT)

Expression	Comment
not 'a' == 'b'	'a' != 'b'
not 'a' > 'b'	'a' <= 'b'
not true	false
not false	true

Implicit conversion to boolean (for advanced uses only!):

Expression	Result	Comment
not -1	false	Negative numbers are truthy.
not 0	true	Zero numbers are falsy.
not 1.23	false	Positive numbers are truthy.
not ""	true	Empty strings are falsy.
not "foo"	false	Non-empty strings are truthy.
not {}	true	Empty sets are falsy.
not {1,2,3}	false	Non-empty sets are truthy.
not null	true	null is falsy.

Disjunction (OR)

Expression	a	b	c	Result	Comment
'a' > 'b' or 'a' > 'c'	1	2	3	false	If both operands are false, false is returned.
'a' > 'b' or 'a' > 'c'	2	1	3	true	If at least one of boolean operands is true, the result is true.
'a' > 'b' or 'a' > 'c'	2	3	1	true	If at least one of boolean operands is true, the result is true.
'a' > 'b' or 'a' > 'c'	3	1	2	true	If- both the operands are true, the result is true.

Advanced uses: Implicit conversion to boolean.

Expression	Result	Comment
"foo" or "bar"	"foo"	If the first operand truthy, it is returned.
"" or false	false	If the first operand is falsy, the second operand is returned.
false or ""	""	If the first operand is falsy, the second operand is returned.

Conjunction (AND)

Expression	a	b	c	Result	Comment
'a' > 'b' and 'a' > 'c'	1	2	3	false	If both operands are false, false is returned.
'a' > 'b' and 'a' > 'c'	2	1	3	false	If at least one of boolean operands is false, the result is false.
'a' > 'b' and 'a' > 'c'	2	3	1	false	If at least one of boolean operands is false, the result is false.
'a' > 'b' and 'a' > 'c'	3	1	2	true	If both the operands are true, the result is true.

Advanced uses: Implicit conversion to boolean.

Expression	Result	Comment
"foo" and "bar"	"bar"	If the first operand truthy, the second operand is returned.
"" and false	""	If the first operand is falsy, it is returned.
false and ""	false	If the first operand is falsy, it is returned.

Conditional Operator

Expression	a	b	Result	Comment
if 'a' > 'b' then "foo" else "bar"	10	5	"foo"	then-value is returned if the condition is satisfied.
if 'a' < 'b' then "foo" else "bar"	10	5	"bar"	else-value is returned if the condition is not satisfied.
if 'a' < 'b' then "foo"			error	else clause must always be present.
if 'a' < 'b' then "foo" else (if 'a' > 'b' then "bar" else "bah")	5	5	"bah"	if-else statements may be nested using parentheses.

Expression	Result	Comment
if -1 then "foo" else "bar"	"foo"	Negative numbers are truthy.
if 0 then "foo" else "bar"	"bar"	Zero numbers are falsy.
if 1.23 then "foo" else "bar"	"foo"	Positive numbers are truthy.
if "" then "foo" else "bar"	"bar"	Empty strings are falsy.
if "bah" then "foo" else "bar"	"foo"	Non-empty strings are truthy.
if {} then "foo" else "bar"	"bar"	Empty sets are falsy.
if {1,2,3} then "foo" else "bar"	"foo"	Non-empty sets are truthy.
if null then "foo" else "bar"	"bar"	null is falsy.