[R] SVM. How to use categorical attributes?

Steve Lianoglou mailinglist.honeypot at gmail.com
Tue Mar 27 20:47:06 CEST 2012


On Tue, Mar 27, 2012 at 6:05 AM, Alekseiy Beloshitskiy
<abeloshitskiy at velti.com> wrote:
> Hi All,
> Here is the case. I want to build classification model (SVM). Some of variables for this model are categorical attributes which represent words  (usually 3-10 words - query for search in google). For example:
> search_id | query_words                        |..| result
> -----------+----------------------------------+--+--------
> 1            | how,to,grow,tree                  |..| 4
> 2            | smartfone,htc,buy,price         |..| 7
> 3            | buy,house,realty,london         |..| 6
> 4            | where,to,go,weekend,cinema |..| 4
> ...
> As you can see, words in the query are disordered and may occur in different queries. Total number of unique words for all queries is several thousands.
> The question is how to represent this variable (query_words) to use for SVM.
> Thank you for any advices!

One approach is to wire up a "bag of words" type of design matrix.

That is to say the matrix has as many columns as there are unique
words. Each row is an observation (query), and the words that appear
in the query have a value of 1 (or you can count the number of times
each word appears).

You can maybe get smarter and try to group like words together, but
... now you'll have two problems ...

Hope you have lots of data!


Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact

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