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Re: Don't show a specific attribute value

by Mark Hall-9 :: Rate this Message:

On 23/06/2009, at 1:20 PM, Andreza Vieira wrote:

>
> Hello,
>
> Please, help me.
> I want to know if there's a way to generate the rules (Weka -
> Association
> Rules) without a specific attribute value. For example: I have an
> attribute
> "play" that can assume "true" or "false", so, I want to generate
> rules that
> contain the attribute "play" with only the "true" value, is not
> interesting
> for me see this attribute with the "false" value.
>
> How can I do it?
>
> I want to do this because I have 50 boolean attributes. So, the Weka
> generates a lot of rules, with several combinations between them,
> that is, a
> lot of not interesting rules.

When processing market basket-type data with Apriori, you need to
encode the data in a specific way to avoid the "uninteresting" rules
that contain the false values. There are several ways to accomplish
this:

1) Standard ARFF format: use single valued attributes (i.e. @attribute
myAtt {true}) and use missing values to indicate that an item is not
present (i.e. missing value instead of "false").

2) In the latest version of Weka with standard ARFF format: use
boolean attributes but make sure that "false" is the first value
declared for each attribute (i.e. @attribute myAtt {false, true}) and
use the -Z option (Treat zero (i.e. first value of nominal attributes)
as missing) with Apriori.

With option 2 you can also use Weka's sparse instances format in order
to save memory. The algorithm runs fractionaly slower when processing
sparse instances.

Cheers,
Mark.

--
Mark Hall
Senior Developer/Consultant, Pentaho Open Source Business Intelligence
Citadel International, Suite 340, 5950 Hazeltine National Dr.,
Orlando, FL 32822, USA
+64 7 847-3537 office, +64 21 399-132 mobile, +1 815 550-8637 fax,
Skype: mark.andrew.hall, Yahoo: mark_andrew_hall
Download the latest release today <http://www.sourceforge.net/projects/pentaho
>

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