[R] vlmc - "In vlmc(traffic.clusters.stationary, cutoff = i) : alphabet with >1-letter strings; trying to abbreviate"

[Constantinos Antoniou]

Dear Martin,

Thank you very much for the (reassuring and helpful) response.

Best regards,
Costas


On Jun 30, 2010, at 3:58 PM, Martin Maechler wrote:

>>>>>> "CA" == Constantinos Antoniou <constantinos.antoniou.rlists at gmail.com>
>>>>>>    on Wed, 30 Jun 2010 12:07:16 +0300 writes:
>>>>>> "CA" == Constantinos Antoniou <constantinos.antoniou.rlists at gmail.com>
>>>>>>    on Wed, 30 Jun 2010 12:07:16 +0300 writes:
> 
>    CA> Dear all (copying the package author),
> 
>    CA> I have a question on the vlmc package. I am trying to
>    CA> model a time series, where each element can take one of
>    CA> 11 values (the result of some clustering). When I run
>    CA> the following command (synthetic data to facilitate
>    CA> self-contained example) 
> 
> (very good)
> 
>> I get the following warning: ("alphabet with >1-letter strings; trying to
>> abbreviate")
> 
>> +++ START+++
>>> library(VLMC)
>>> a <- floor(runif(1000,0,11))
>>> vc <- vlmc(a,cutoff=5)
>> Warning message:
>> In vlmc(a, cutoff = 5) :
>> alphabet with >1-letter strings; trying to abbreviate
>>> vc
>> 'vlmc' a Variable Length Markov Chain;
>> alphabet 'abcdefghijk', |alphabet| = 11, n = 1000.
>> Call: vlmc(dts = a, cutoff.prune = 5)
>    -> extensions (= $size ) :
>> ord.MC   context nr.leaves     total 
>> 2        72        61      1608 
>> AIC =  5247 
>>> 
>> +++ END+++
> 
>> The questions are: 
>> 1. What is it trying to do? 
> 
> Your contains values  0 1 2 .. 10
> it tries to match them to 1-letter strings, but '10' "is 2
> letters"
> 
>> 2. How is it abbreviating? 
> 
> (not really important: using abbreviate() 
> 
>> 3. How much should I worry about it?
> 
> not at all.  The warning is just to inform you that your input
> looks a bit "unusual" to vlmc.
> 
> I do agree however, that one could argue that vlmc() should work
> for inputs with values
>     0:m
> or   1:n
> without a warning.
> 
>> 4. What can I do?
> 
> You could use 
> 
>    vc <- vlmc(letters[1+a], cutoff=5)
> 
> to get the exact same model, but without a warning.
> or
>    vc <- vlmc(a, cutoff=5, quiet = TRUE)
> or
>    vc <- vlmc(a, cutoff=5, code1char = FALSE)
> 
> 
> 
>> I have looked at the documentation plus 
>> M<c3><a4>chler M. and B<c3><bc>hlmann P. (2004) Variable Length Markov Chains:
>> Methodology, Computing, and Software.  _J. Computational and
>> Graphical Statistics_ *2*, 435-455.
> 
> That's good. 
> The examples there all have a character vector (of
> strings with 1 letter/character) as input.
> 
> 
>> Thanks for any feedback,
> 
> You're welcome!
> Martin Maechler, ETH Zurich
> 
> 
>> -- 
>> Constantinos Antoniou, Ph.D., Assistant Professor
>> National Technical University of Athens
>> Laboratory of Transportation Engineering 
>> School of Rural and Surveying Engineering
>> 9 Heroon Politechniou st., 15780-Zografou, Athens, Greece
>> T: +30 210 7722783 - F: +30 210 7722629 
>> antoniou at central.ntua.gr - http://users.ntua.gr/antoniou
> 
> 
>> Dear all (copying the package author), I have a question
>> on the vlmc package. I am trying to model a time series,
>> where each element can take one of 11 values (the result
>> of some clustering). When I run the following command
>> (synthetic data to facilitate self-contained example) I
>> get the following warning: ("alphabet with >1-letter
>> strings; trying to abbreviate")
> 
> 
> 
>> +++ START+++
>>> library(VLMC) a <- floor(runif(1000,0,11)) vc <-
>>> vlmc(a,cutoff=5)
>> Warning message: In vlmc(a, cutoff = 5) : alphabet with
>>> 1-letter strings; trying to abbreviate
>>> vc
>> 'vlmc' a Variable Length Markov Chain; alphabet
>> 'abcdefghijk', |alphabet| = 11, n = 1000.  Call:
>> vlmc(dts = a, cutoff.prune = 5)
>    -> extensions (= $size ) :
>>   ord.MC context nr.leaves total 2 72 61 1608 AIC =
>> 5247
>>> 
>> +++ END+++
> 
>> The questions are: 1. What is it trying to do?  2. How
>> is it abbreviating?  3. How much should I worry about
>> it?  4. What can I do?
> 
>> I have looked at the documentation plus M<c3><a4>chler
>> M. and B<c3><bc>hlmann P. (2004) Variable Length Markov
>> Chains: Methodology, Computing, and Software.
>> _J. Computational and Graphical Statistics_ *2*,
>> 435-455.
> 
> 
>> Thanks for any feedback, Costas
> 
> 
> 
>> -- Constantinos Antoniou, Ph.D., Assistant Professor
>> National Technical University of Athens Laboratory of
>> Transportation Engineering School of Rural and Surveying
>> Engineering 9 Heroon Politechniou st., 15780-Zografou,
>> Athens, Greece T: +30 210 7722783 - F: +30 210 7722629
>> antoniou at central.ntua.gr - http://users.ntua.gr/antoniou
> 
>