R help - Jan 2013 - plot.mob() fails with cut() error "'breaks' are not unique"

DeaR all,

I am using mob() for model based partitioning, with a dichotomous variable
(participant's correct/incorrect response to a test item) regressed onto a
continuous predictor related to a given property of the test item. Although this
variable is continuous, the value of this variable for many items in this
particular analysis is 0. The partitioning criterion is self-reported ability in
a related area.
> mob1 <- mob(
    correct ~ circular.mean | srp.dimension,
    control=mob_control(alpha=.001),
    model=glinearModel,
    family=binomial()
  )
> plot(mob1)
Error in cut.default(x, breaks = breaks, include.lowest = TRUE) : 
  'breaks' are not unique

The same persists if I specify either a desired number of breaks, or explicit
breakpoints (e.g. breaks=3 or breaks=c(-0.1,0.1,0.5)). I guess this is to do
with the funny distribution of the predictor variable, but I'm not sure what
to do about it.

Many thanks and apologies if this doesn't fit the mailing list---it is my
first posting!
Jason Musil

On Tue, 22 Jan 2013, Jason Musil wrote:
> DeaR all,
>
> I am using mob() for model based partitioning, with a dichotomous 
> variable (participant's correct/incorrect response to a test item) 
> regressed onto a continuous predictor related to a given property of the 
> test item. Although this variable is continuous, the value of this 
> variable for many items in this particular analysis is 0. The 
> partitioning criterion is self-reported ability in a related area.
>
>> mob1 <- mob(
>    correct ~ circular.mean | srp.dimension,
>    control=mob_control(alpha=.001),
>    model=glinearModel,
>    family=binomial()
>  )
>
>> plot(mob1)
>
> Error in cut.default(x, breaks = breaks, include.lowest = TRUE) :
>  'breaks' are not unique
>
> The same persists if I specify either a desired number of breaks, or 
> explicit breakpoints (e.g. breaks=3 or breaks=c(-0.1,0.1,0.5)). I guess 
> this is to do with the funny distribution of the predictor variable, but 
> I'm not sure what to do about it.
Jason, you can't pass the "breaks" argument to the plot method
directly
but need to pass it on to the panel function drawing the terminal panels. 
As an example consider

example("mob")
plot(fmPID)
plot(fmPID, tp_args = list(breaks = c(0, 100, 120, 200)))

Hope that fixes your problem.

Best,
Z
> Many thanks and apologies if this doesn't fit the mailing list---it is
my first posting!
> Jason Musil
>
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