R help - Sep 2008 - rpart with only two small groups

Hello R-User!

I try to do the following:

New<-iris[c(1:7,90:97),1:5]
New.rpart<-rpart(Species~., data=New, method="class")

New.rpart
n= 15 

node), split, n, loss, yval, (yprob)
      * denotes terminal node

1) root 15 7 versicolor (0.4666667 0.5333333) *

Does it mean it is not possible to find a variable that splits my groups or
are my groups just to small?
Is there a way to find out the variable that splits my groups best?

Thanks in advance for help.

B.

-----
The art of living is more like wrestling than dancing.
(Marcus Aurelius)
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On Tue, 2008-09-16 at 10:47 -0700, Birgitle wrote:
> Hello R-User!
> 
> I try to do the following:
> 
> New<-iris[c(1:7,90:97),1:5]
> New.rpart<-rpart(Species~., data=New, method="class")
> 
> New.rpart
> n= 15 
> 
> node), split, n, loss, yval, (yprob)
>       * denotes terminal node
> 
> 1) root 15 7 versicolor (0.4666667 0.5333333) *
> 
> Does it mean it is not possible to find a variable that splits my groups or
> are my groups just to small?
> Is there a way to find out the variable that splits my groups best?
Yes, as always, read the help file ;-)

?rpart leads you to ?rpart.control, which has argument minsplit with
default 20, which is the minimum number of observations in a node for a
split to be attempted. As 15 is less than 20, the root node could not be
split.

E.g.:
> New<-iris[c(1:7,90:97),1:5]
> New.rpart<-rpart(Species~., data=New, method="class", control
rpart.control(minsplit = 2))
> New.rpart
n= 15 

node), split, n, loss, yval, (yprob)
      * denotes terminal node

1) root 15 7 versicolor (0.4666667 0.5333333)  
  2) Petal.Length< 2.5 7 0 setosa (1.0000000 0.0000000) *
  3) Petal.Length>=2.5 8 0 versicolor (0.0000000 1.0000000) *

HTH

G
> 
> Thanks in advance for help.
> 
> B.
> 
> -----
> The art of living is more like wrestling than dancing.
> (Marcus Aurelius)
-- 
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
 Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
 ECRC, UCL Geography,          [f] +44 (0)20 7679 0565
 Pearson Building,             [e] gavin.simpsonATNOSPAMucl.ac.uk
 Gower Street, London          [w] http://www.ucl.ac.uk/~ucfagls/
 UK. WC1E 6BT.                 [w] http://www.freshwaters.org.uk
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%

Thanks Gavin and sorry to all for this unnecessary question.

B.


Gavin Simpson wrote:
> 
> On Tue, 2008-09-16 at 10:47 -0700, Birgitle wrote:
>> Hello R-User!
>> 
>> I try to do the following:
>> 
>> New<-iris[c(1:7,90:97),1:5]
>> New.rpart<-rpart(Species~., data=New, method="class")
>> 
>> New.rpart
>> n= 15 
>> 
>> node), split, n, loss, yval, (yprob)
>>       * denotes terminal node
>> 
>> 1) root 15 7 versicolor (0.4666667 0.5333333) *
>> 
>> Does it mean it is not possible to find a variable that splits my
groups
>> or
>> are my groups just to small?
>> Is there a way to find out the variable that splits my groups best?
> 
> Yes, as always, read the help file ;-)
> 
> ?rpart leads you to ?rpart.control, which has argument minsplit with
> default 20, which is the minimum number of observations in a node for a
> split to be attempted. As 15 is less than 20, the root node could not be
> split.
> 
> E.g.:
>> New<-iris[c(1:7,90:97),1:5]
>> New.rpart<-rpart(Species~., data=New, method="class",
control > rpart.control(minsplit = 2))
>> New.rpart
> n= 15 
> 
> node), split, n, loss, yval, (yprob)
>       * denotes terminal node
> 
> 1) root 15 7 versicolor (0.4666667 0.5333333)  
>   2) Petal.Length< 2.5 7 0 setosa (1.0000000 0.0000000) *
>   3) Petal.Length>=2.5 8 0 versicolor (0.0000000 1.0000000) *
> 
> HTH
> 
> G
> 
>> 
>> Thanks in advance for help.
>> 
>> B.
>> 
>> -----
>> The art of living is more like wrestling than dancing.
>> (Marcus Aurelius)
> -- 
> %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
>  Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
>  ECRC, UCL Geography,          [f] +44 (0)20 7679 0565
>  Pearson Building,             [e] gavin.simpsonATNOSPAMucl.ac.uk
>  Gower Street, London          [w] http://www.ucl.ac.uk/~ucfagls/
>  UK. WC1E 6BT.                 [w] http://www.freshwaters.org.uk
> %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 

-----
The art of living is more like wrestling than dancing.
(Marcus Aurelius)
-- 
View this message in context:
http://www.nabble.com/rpart-with-only-two-small-groups-tp19516515p19526594.html
Sent from the R help mailing list archive at Nabble.com.