Message-ID: <47F09DD1.1080905@sanbi.ac.za>
Date: Mon, 31 Mar 2008 10:16:17 +0200
From: Allan Kamau <allank@sanbi.ac.za>
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To: pgsql-sql@postgresql.org
Subject: Removing redundant itemsets
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Hi all,
I have a list of purchases (market basket) and I would like to select
non redundant longest possible patterns by eliminating
(creating/populating other table to contain only non redandant itemsets)
purchases having item lists which are fully included in at least one
other purchase.

(Am assuming all the items of all the purchases have met the minimum
support currently set at 1)

Below is a sample case, table schema and data(DDL and DML)

Transaction   Itemset
'100'               'a','b','c','d'
'200'               'c','d'
'300'               'a','c','e'
'400'               'e','d'

On successful removal out of 'redanduant' or smaller purchases having
items contained in totality by at least one other purchase, the
purchase '200' would be weeded out as it's itemset {'c','d'} is
contained in '100' {'a','b','c','d'} purchase.


drop sequence if exists togo_seq cascade;
create sequence togo_seq;
drop table if exists togo cascade;
create table togo
(
id integer not null default nextval('togo_seq')
,tid char(3) not null
,item char(1) not null
,primary key(id)
,unique(tid,item)
)
;
insert into togo(tid,item)values('100','b');
insert into togo(tid,item)values('100','a');
insert into togo(tid,item)values('100','c');
insert into togo(tid,item)values('100','d');
insert into togo(tid,item)values('200','c');
insert into togo(tid,item)values('200','d');
insert into togo(tid,item)values('300','a');
insert into togo(tid,item)values('300','c');
insert into togo(tid,item)values('300','e');
insert into togo(tid,item)values('400','e');
insert into togo(tid,item)values('400','d');

Allan.