R help - Nov 2014 - Strange error while passing string as an argument to the function in bnlearn package

Hello everybody,

I am working with the package bnlear, but, probably, error is caused not by
the package itself.

There is a function cpquery() to which I pass argument str2:

str2="(lag1=='s')"
prob.s = cpquery(fitted1,
                            
event=eval(parse(text="(M=='s')")),
                             evidence=eval(parse(text=str2)))

- Error in parse(text = str2) : object 'str2' not found

fitted1 is a fitted model

But if I put value of str2 directly into function call:

prob.s = cpquery(fitted1,
                            
event=eval(parse(text="(M=='s')")),
                             evidence="(lag1.M1=='s')")
it works fine.

Does anybody have any idea how to fix it?

PS:
- I used documentation to the package:
http://cran.r-project.org/web/packages/bnlearn/bnlearn.pdf
function cpquery()
- I also trued to use backslashes \' \" - doesn't work too

-- 
Best regards,
Alexandr

	[[alternative HTML version deleted]]

Hi Alexandr,

On 10 November 2014 17:46, Alexandr M <rus314 at gmail.com>
wrote:
> I am working with the package bnlear, but, probably, error is caused not by
> the package itself.
Logic sampling in cpquery() relies on handling unevaluated
expressions, so it is a tad fragile in any complex setting (inside
loops and function calls, for example). On its own, the
eval(parse(...)) trick works if you do it in the global environment,
or in relatively simple scripts.

For the simple query you are trying to do, just use likelihood weighting:

prob.s = cpquery(fitted1,
                            
event=eval(parse(text="(M=='s')")),
                             evidence=list(lag1.M1='s'),
                             method = "lw")

passing str2 as a list.

Cheers,
    Marco

-- 
Marco Scutari, Ph.D.
Lecturer in Statistics, Department of Statistics
University of Oxford, United Kingdom