Compare average - SPARQL -

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there dataset of users ranking movies. need find users similar taste user1. similar taste defined follows: consider average rank genre user1 avgr1 , same genre user2 avgr2, user1 , user2 have similar taste abs(avgr1-avgr2)<1 . far able names, genre , absolute value between averages, filtering comparison not working. 

select ?p ?p1 ?genre (abs (avg(?rating)-avg(?ratingp1)) ?rdiff) where{ ?p movies:hasrated ?rate. ?p1 foaf:knows ?p. ?rate movies:ratedmovie ?mov. ?rate movies:hasrating ?rating. ?mov movies:hasgenre ?genre. ?p1 movies:hasrated ?ratep1. ?ratep1 movies:ratedmovie ?movp1. ?ratep1 movies:hasrating ?ratingp1. ?movp1 movies:hasgenre ?genre. filter (xsd:float(?rdiff)<1.0 && ?p=movies:user1) } group ?p ?p1 ?genre

it's hard answer these kinds of questions without sample data work with. here's sample data has 2 users have similar rankings on comedy, different rankings on romance:

@prefix : <urn:ex:>  :a :ranks [ :genre :comedy ; :value 2 ],           [ :genre :comedy ; :value 3 ],           [ :genre :comedy ; :value 3 ],           [ :genre :romance ; :value 7 ],           [ :genre :romance ; :value 8 ],           [ :genre :romance ; :value 9 ].  :b :ranks [ :genre :comedy ; :value 3 ],           [ :genre :comedy ; :value 3 ],           [ :genre :comedy ; :value 4 ],           [ :genre :romance ; :value 0 ],           [ :genre :romance ; :value 1 ],           [ :genre :romance ; :value 0 ].

here's query computes difference of average rankings on genres:

prefix : <urn:ex:>  select ?user1 ?user2 ?genre (abs(avg(?value1)-avg(?value2)) ?diff) {   ?user1 :ranks [ :genre ?genre ; :value ?value1 ].   ?user2 :ranks [ :genre ?genre ; :value ?value2 ].   filter (str(?user1) < str(?user2)) #-- avoid duplicate user1/user2, user2/user1 results } group ?user1 ?user2 ?genre order ?diff 
--------------------------------------------------------- | user1 | user2 | genre    | diff                       | ========================================================= | :a    | :b    | :comedy  | 0.666666666666666666666667 | | :a    | :b    | :romance | 7.666666666666666666666667 | ---------------------------------------------------------

now, can't filter on aggregate results, have use having, take values diff less particular value, you'd this:

prefix : <urn:ex:>  select ?user1 ?user2 ?genre (abs(avg(?value1)-avg(?value2)) ?diff) {   ?user1 :ranks [ :genre ?genre ; :value ?value1 ].   ?user2 :ranks [ :genre ?genre ; :value ?value2 ].   filter (str(?user1) < str(?user2)) } group ?user1 ?user2 ?genre having (?diff < 1) order ?diff 
-------------------------------------------------------- | user1 | user2 | genre   | diff                       | ======================================================== | :a    | :b    | :comedy | 0.666666666666666666666667 | --------------------------------------------------------

if don't care actual diff, except it's below threshold, can put expression in having directly, , do:

select ?user1 ?user2 ?genre {   #-- ... } group ?user1 ?user2 ?genre having (abs(avg(?value1)-avg(?value2)) < 1)

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