7/27/2019 Computational Journalism at Columbia, Fall 2013, Lecture 5: Hybrid Filtering

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Fron%ersof

Computa%onalJournalism

ColumbiaJournalismSchool

Week5:HybridFiltersOctober2,2013

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Week5:HybridFiltering

FilteringCommentsbyVo%ng

User-itemrecommenda%onsystems

GeneralHybridFilters

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FilteringComments

Thousandsofcomments,whatarethegoodones?

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Commentvo%ng

Problem:pungcommentswithmostvotesattopdoesntwork.Why?

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RedditCommentRanking

Hypothe%cally,supposeallusersvotedonthecomment,andvoutofNup-voted.Thenwecouldsort

bypropor%onp=v/Nofupvotes.

N=16

v=11

p=11/16=0.6875

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RedditCommentRanking

Actually,onlynusersoutofNvote,givinganobserved

approximatepropor%onp=v/n

n=3

v=1

p=1/3=0.333

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RedditCommentRanking

Limitedsamplingcanrankvoteswrongwhenwedont

haveenoughdata.

p=0.333

p=0.6875

p=0.75

p=0.1875

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Randomerrorinsampling

Ifweobservepupvotesfromnrandomusers,whatisthedistribu%onofthetruepropor%onp?

Distribu%onofpwhenp=0.5

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Confidenceinterval

Givenobservedp,intervalthattruephasa

probabilityoflyinginside.

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Week5:HybridFiltering

FilteringCommentsbyVo%ng

User-itemrecommenda%onsystems

GeneralHybridFilters

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User-itemmatrix

Storesra%ngofeachuserforeachitem.Couldalso

bebinaryvariablethatsayswhetheruserclicked,liked,

starred,shared,purchased...

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User-itemmatrix

Nocontentanalysis.Weknownothingaboutwhatisineachitem.

Typicallyverysparseauserhasntwatchedeven1ofallmovies.

Filteringproblemisguessingunknownentryinmatrix.Highguessedvaluesarethingsuser

wouldwanttosee.

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Filteringprocess

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Howtoguessunknownra%ng?

Basicidea:suggestsimilaritems.

Similaritemsareratedinasimilarwaybymany

differentusers.

Remember,ra%ngcouldbeaclick,alike,a

purchase. UserswhoboughtAalsoboughtB... UserswhoclickedAalsoclickedB... UserswhosharedAalsosharedB...

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Similaritems

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Itemsimilarity

Cosinesimilarity!

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Otherdistancemeasures

adjustedcosinesimilarity

Subtractsaveragera%ngforeachuser,tocompensate

forgeneralenthusiasm(mostmoviessuckvs.most

moviesaregreat)

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Genera%ngarecommenda%on

Weightedaverageofitemra%ngsbytheirsimilarity.

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Week5:HybridFiltering

FilteringCommentsbyVo%ng

User-itemrecommenda%onsystems

GeneralHybridFilters

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DifferentFilteringSystems

Purealgorithmic:Newsblasteranalyzethetopicsinthedocuments.Noconceptofusers.

Puresocial:WhatIseeonTwierdeterminedbywhoI

follow.Nocontentanalysis.

Hybrid:Redditcommentsfilteredbyanalgorithmthattakesvotesasinput.

Hybrid:Itemsrecommendedbasedco-consump%onbyallusers.

Whatelseispossible?

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ItemContent MyData OtherUsersData

Textanalysis,topic

modeling,clustering...

whoIfollow

whatIveread/liked

socialnetworkstructure,

otheruserslikes

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Howtoevaluate/op%mizethefilter?

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Howtoevaluate/op%mizethefilter?

Nelix:trytopredictthera%ngthattheusergivesamovieaerwatchingit.

Amazon:sellmorestuff. Googlewebsearch:humanratersA/Btesteverychange