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# nominal vs polynominal

Member Posts: 24 Maven
edited November 2018 in Help
what, if anything, is the difference in polynominal and nominal?

They are offered as separate types, but appear to be used interchangeably, at least in some cases.

thanks!

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Moderator, Employee, Member Posts: 295 RM Product Management
Hi,

polynominal is a subtype of nominal. A nominal value may be either polynominal or binominal, the first meaning there are more than 2 distinct values, the latter one meaning there are exactly two values. Hence, a polynominal value is always a nominal one, but this is not true the other way round.

Kind regards,
Tobias
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Member Posts: 24 Maven
OK, thanks.

Then, there should be no reason to assign an attribute to the nominal type.  It should either be set to binomial or polynomial.

Correct?
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Administrator, Moderator, Employee, RapidMiner Certified Analyst, RapidMiner Certified Expert, Community Manager, RMResearcher, Member, University Professor Posts: 1,751 RM Founder
Hi,

principally, yes. On the other hand, there is currently no operator available who distinguishes between nominal and polynominal. From an algorithmic point of view, if an operator supports more than two values it also supports two as well. Hence, in most places you will not find any distinction between polynominal and nominal.

Cheers,
Ingo
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Member Posts: 24 Maven
Thank you.  That is very helpful to know.
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Member Posts: 1 Contributor I
Hi
Then, what is the difference between nominal, polynominal and binominal? If the nominal type is polynominal or binominal, why exists the nominal type?
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RapidMiner Certified Expert, Member Posts: 1,869 Unicorn
Polynominal and nominal are identical in the current implementation, so they are interchangeable. In fact the nominal type could be hidden from the users, but for historical reasons it is not. Binominal is different in that a binominal attribute can have at most 2 different values.

Best regards,
Marius