[R] error in random forest

[Nagu]

Thank you very much. I'll jump in to the data and verify the
consistency between the training and testing variables and their
levels.

On Fri, Mar 7, 2008 at 5:14 PM,  <Bill.Venables at csiro.au> wrote:
> The error message is pretty clear, really.  To spell it out a bit more,
>  what you have done is as follows.
>
>  Your training set has factor variables in it.  Suppose one of them is
>  "f".  In the training set it has 5 levels, say.
>
>  Your test set also has a factor "f", as it must, but it appears that in
>  the test set it has 6 levels, or more, or levels that do not agree with
>  those for "f" in the training set.
>
>  This mismatch measn that the predict method for randomForest cannot use
>  this test set.
>
>  What you have to do is make sure that the factor levels agree for every
>  factor in both test and training set. One way to do this is to put the
>  test and training set together with rbind(...) say, and then separate
>  them again.  But even this will still have a problem for you.  Because
>  you training set will have some factor levels empty, which are not empty
>  in the test set.  The error will most likely be more subtle, though.
>
>  You really need to sort this out yourself.  It is not particularly an R
>  problem, but a confusion over data.  To be useful, your training set
>  need to cover the field for all levels of every factor.  Think about it.
>
>
>
>  -----Original Message-----
>  From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
>  On Behalf Of Nagu
>  Sent: Saturday, 8 March 2008 5:37 AM
>  To: r-help at r-project.org; r-help at stat.math.ethz.ch
>  Subject: [R] error in random forest
>
>  Hi,
>
>  I get the following error when I try to predict the probabilities of a
>  test sample:
>
>  Error in predict.randomForest(fit.EBA.OM.rf.50, x.OM, type = "prob") :
>   New factor levels not present in the training data
>
>  I have about 630 predictor variables in the dataset x.OM (25 factor
>  variables and the remaining are continuous variables). Any ideas on
>  how to trace it?
>
>  Thank you,
>  Nagu
>
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>