"SOM (SOMDimensionality Reduction) documentation or examples"

User401

Hi all,
I'm looking into the use of RMiner's SOM. I can get it to produce nice looking results but would like more information on its setup and interpreting the type of results in RMiner.

Does anyone have any worked examples or documentation? I'm wondering, in particular, how to interpret the resulting plot view and data view, relating the points back to the original data features.

I'd be very grateful for any help.

Thanks,
Richie

haddock

Hi Richie,

I think I told you in a previous post that RM is much better than its documentation, this is a case in point. Try this code, and waft your mouse over the data points of your SOM plot ( coloured by label probably ), behold the Ids!

<operator name="Root" class="Process" expanded="yes">
    <operator name="ExampleSetGenerator" class="ExampleSetGenerator">
        <parameter key="target_function"	value="random"/>
    </operator>
    <operator name="IOMultiplier" class="IOMultiplier">
        <parameter key="io_object"	value="ExampleSet"/>
    </operator>
    <operator name="IdTagging" class="IdTagging">
        <parameter key="create_nominal_ids"	value="true"/>
    </operator>
    <operator name="SOMDimensionalityReduction" class="SOMDimensionalityReduction">
    </operator>
</operator>

While the human eyeball mk.IV is about as smart as it gets in terms of finding and enjoying patterns, it sometimes may like patterns that are not helpful; in this latter case wheel out some horrible counting stuff to give the semblance of reason. In your context it is a matter of checking that the reduction produces "better" performance. So cross validate a learner on the original dataset, then reduce it and repeat the process. If it does, even after you've messed around with genetic optimisers etc.etc.., then you may have found an abstraction.  ;D

I stress the phrase "semblance of reason", because no matter what you do you will be left with doubt, known here as the "Curse of MIerswa" - did you realise that "Ingo Mierswa" can be rearranged as "imagine rows"?

dubito ergo sum ("I doubt, therefore I exist") and si fallor sum ("If I am deceived, I exist")

Augustine of Hippo

Ergo clearly a dataminer.