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EFIM-closed and backward extension checking
Posted by: frank
Date: November 06, 2020 11:01AM

Dear Sir
i read the EFIM algorithm and i understand it because of the compleate example on page 20 is it possible to take an example like EFIM example for EFIM close Algorithm?
Kind Regards



Edited 1 time(s). Last edit at 11/13/2020 08:38AM by webmasterphilfv.

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Re: EFIM
Date: November 07, 2020 05:14AM

Hi,

Glad the article has been helpful to understnad the algorithm.

I currently do not have detailed example for the EFIM-Closed algorithm and these days I am overloaded with work so I cannot really prepare one. But there is also a PPT presentation about this algorithm:

http://www.philippe-fournier-viger.com/EFIM_and_EFIM-Closed_high_utility_mining.pdf

It contains a few slides about EFIM-Closed towards the end. Maybe it can be helpful.

Besides that, if you run the Java code of EFIM-Closed with a debugger, you can see everything that happens step by step!

If you some question about some specific definition in EFIM-Closed, maybe I can answer if the question is simple and clear about some precise aspect of the algorithm.

Best regards,

Philippe

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Re: EFIM
Posted by: frank
Date: November 12, 2020 09:09AM

Hi
thank you for help.in line 4 of algorithm 2 in efim close when we want to check backward extention of item beta we scan database alfa-D or beta-D?
Regards

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Re: EFIM
Date: November 13, 2020 08:34AM

frank Wrote:
-------------------------------------------------------
> Hi
> thank you for help.in line 4 of algorithm 2 in
> efim close when we want to check backward
> extention of item beta we scan database alfa-D or
> beta-D?
> Regards


Hi Frank,

I will explain a bit. We have an itemset BETA and we want to check if it is closed. Thus we will check if it has a backward extension or if it has a forward extension.

To check if BETA has a backward extension, we need to check all transactions that contain BETA. So this means that we need to check all transactions that are in BETA-D. However, it is important to note that we dont really use the transations as they are in BETA-D. We instead use the ORIGINAL transactions that correspond to those in BETA-D.

Why? The reason is that the transactions in BETA-D have been cut (some items have been removed) when doing the projection. But when we check for backward extensions, we need to be able to check the items that have been removed. So we check all original transactions that correspond to those in BETA-D.

For example if BETA = C

And the original database is:
Transaction 1 : A B C D E
Transaction 2 : A B C E F
Transaction 3 : A B G

and the total order is A < B < C < D < E < F,

the projected database of BETA is:

Transaction 1 : D E
Transaction 2 : E F

If we want to check if BETA has a backward extension, we need to check all the transactions in the BETA-projected-database, that is transactions 1 and 2.

Transaction 1 : D E
Transaction 2 : E F

However, we will check for backward extensions of BETA using the corresponding original transactions:

Transaction 1 : A B C D E
Transaction 2 : A B C E F

and we will find that A appears 2 times and B appear two times...

Thus BETA has two backward extensions. The first one is the item A. The second one is the item B.

Hope that this helps



Edited 2 time(s). Last edit at 11/13/2020 08:37AM by webmasterphilfv.

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