Amber Dawn Nolder wrote 2014-05-28 23:16:
Hello,
I am an R novice, and I am using the "partykit" package to create
regression trees. I used the following to generate the trees:
ctree(y~x1+x2+x3+x4,data=my_data,control=ctree_control(testtype =
"Bonferroni", mincriterion = 0.90, minsplit = 12, minbucket = 4,
majority = TRUE)
I thought that "minbucket" set the minimum value for the sum of weights
in each terminal node, and that each case weight is 1, unless otherwise
specified. In which case, the sum of case weights in a node should equal the
number of cases (n) in that node. However, I sometimes obtain a tree with
a terminal node that contains fewer than 4 cases.
I do agree that the tree below looks suspicious. You may have found a
bug.
But you didn't provide "commented, minimal, self-contained, reproducible
code", i.e., we're missing your 'my_data' object, and therefore we
cannot reproduce this easily. Can you please provide us with the output
from 'dput(my_data)'?
My data set has a total of 36 cases. The dependent and all independent
variables are continuous data. Variables x1 and x2 contain missing (NA)
values.
I tried a few other data sets and there the results seem to come out OK
(even after inducing NAs).
Could someone please explain why I am getting these results?
Probably. But you need to provide a reproducible example and the
details obtained by 'sessionInfo()'.
As per the posting guide, since this is a contributed package you should
first contact its maintainer (Torsten Hothorn, CC'd) and only post here
if you get no reply. Did you try contacting Torsten?
Am I mistaken about the value of case weights or about the use of minbucket
to restrict the size of a terminal node?
I don't think you're mistaken since '?ctree_control' says that
"minbucket: the minimum sum of weights in a terminal node."
Henric
This is an example of the output:
Model formula:
y ~ x1 + x2 + x3 + x4
Fitted party:
[1] root
| [2] x4 <= 30: 0.927 (n = 17, err = 1.1)
| [3] x4 > 30
| | [4] x2 <= 43: 0.472 (n = 8, err = 0.4)
| | [5] x2 > 43
| | | [6] x3 <= 0.4: 0.282 (n = 3, err = 0.0)
| | | [7] x3 > 0.4: 0.020 (n = 8, err = 0.0)
Number of inner nodes: 3
Number of terminal nodes: 4
Many thanks!
Amber Nolder
Graduate Student
Indiana University of Pennsylvania
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and provide commented, minimal, self-contained, reproducible code.
