Filter

Here be functions that filter out objects.

range

A filter that emits the objects within a range.

(q/query (g/find-by-id 1)
         (q/-->)
         (q/into-vec!))
;= [#<TinkerVertex v[2]> #<TinkerVertex v[4]> #<TinkerVertex v[3]>]         
;; To emit only the first and second objects:

(q/query (g/find-by-id 1)
         (q/-->)
         (q/range 0 1)
         (q/into-vec!))
;= [#<TinkerVertex v[2]> #<TinkerVertex v[4]>]

dedup

Filter out repeated objects. A function can be supplied that provides the values that the pipeline will consider when filtering 

(q/query (g/get-vertices)
         q/<->
         (q/property :name)
         (q/into-vec!))         
;= ["marko" "josh" "peter" "marko" "vadas" "josh" "lop" "lop" "josh" "marko" "ripple" "lop"]

(q/query (g/get-vertices)
         q/<->
         q/dedup
         (q/property :name)
         (q/into-vec!))
;= ["marko" "josh" "peter" "vadas" "lop" "ripple"]                         

(q/query (g/get-vertices)
          q/<->
          (q/dedup (partial g/get-property :lang))
          (q/property :name)
          (q/into-vec!))
;= ["marko" "lop"]

Note that g/get-vertices retrieves all of the vertices of the graph and provides them in a list.

except

Filter out the provided objects.

(q/query (g/find-by-id 1)
         q/-->
         q/<--
         (q/except [(g/find-by-id 1)])
         (q/into-vec!))         
;= [#<TinkerVertex v[4]> #<TinkerVertex v[6]>]

filter

Uses a predicate to decide whether an object should pass.

(q/query (g/get-vertices)
         (q/filter (fn [v] (= "java" (.getProperty v "lang"))))
         q/map
         (q/all-into-maps!))         
;= ({:name "lop", :lang "java"} {:name "ripple", :lang "java"})

has

Allows an element if it has a particular property. The standard Clojure operations for comparisons can also be supplied: >,>=,<,<=,=,not=. 

(q/query (g/get-vertices)
         (q/has :name "marko")
         (q/map)
         (q/into-vec!))
;= [{"age" 29, "name" "marko"}]

(q/query (g/get-vertices)
         (q/has :age > (int 30))
         (q/map)
         (q/into-vec!))
;= [{"age" 35, "name" "peter"} {"age" 32, "name" "josh"}]

When no value is supplied, has filters out objects where the specified keys is not present:

(q/query (g/get-vertices)
         (q/has :age)
         (q/map)
         (q/into-vec!))

has-not

Allows an element if it does not have a particular property. 

(q/query (g/get-vertices)
         (q/has-not :age)
         (q/map)
         (q/into-vec!))
;= [{"name" "lop", "lang" "java"} {"name" "ripple", "lang" "java"}]

(q/query (g/get-vertices)
         (q/has-not :name "marko")                    
         (q/map)
         (q/into-vec!))
;= [{"name" "lop", "lang" "java"} 
;=  {"age" 27, "name" "vadas"}
;=  {"age" 35, "name" "peter"}
;=  {"name" "ripple", "lang" "java"}
;=  {"age" 32, "name" "josh"}]

Note that Gremlin does not support has-not with a comparator other than equlity.

interval

Allow elements to pass that have their property in the provided start and end interval.

(q/query (g/find-by-id 1)
         (q/-E>)
         (q/interval :weight 0 0.6)
         (q/in-vertex)
         (q/into-vec!))
;= [#<TinkerVertex v[2]> #<TinkerVertex v[3]>]

random

Emits the incoming objects, each with the supplied chance.

;=   Results may vary
(q/query (g/get-vertices)
         (q/random 0.5)
         (q/into-vec!))
;= [#<TinkerVertex v[6]> #<TinkerVertex v[4]>]

(q/query (g/get-vertices)
         (q/random 0.5)
         (q/into-vec!))
;= [#<TinkerVertex v[3]> #<TinkerVertex v[1]> #<TinkerVertex v[6]> #<TinkerVertex v[4]>]

retain

Only allows elements in the supplied collection to pass.

(q/query (g/find-by-id 1)
         (q/-->)      
         (q/retain [(g/find-by-id 2)])
         (q/into-vec!))
;= [#<TinkerVertex v[2]>]

Annotating pipes is next

You should read about annotating pipes next.

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