[R] Using trace

[ronggui]

Here is a partial solution:

> trace(fact,quote({cat(sprintf("x= %i\n",x));return}),print=T)
[1] "fact"
> fact(4)
Tracing fact(4) on entry
x= 4
Tracing fact(x - 1) on entry
x= 3
Tracing fact(x - 1) on entry
x= 2
Tracing fact(x - 1) on entry
x= 1
Tracing fact(x - 1) on entry
x= 0
[1] 24


2009/4/17 Stavros Macrakis <macrakis at alum.mit.edu>:
> Well, yes, of course I could add the code to the function by hand.  I
> could also calculate square roots by hand.  But -- as in every other
> basic programming environment -- there exists an R function 'trace'
> which appears to automate the process, and I can't figure out how to
> use it to handle this most elementary and standard case.  Clearly I'm
> missing something.
>
>              -s
>
> On Thu, Apr 16, 2009 at 9:26 PM, ronggui <ronggui.huang at gmail.com> wrote:
>> Can you just print what you need to know? For example:
>>
>>> fact <- function(x) {
>> + if(x<1) ans <- 1 else ans <- x*fact(x-1)
>> + print(sys.call())
>> + cat(sprintf("X is %i\n",x))
>> + print(ans)
>> + }
>>> fact(4)
>> fact(x - 1)
>> X is 0
>> [1] 1
>> fact(x - 1)
>> X is 1
>> [1] 1
>> fact(x - 1)
>> X is 2
>> [1] 2
>> fact(x - 1)
>> X is 3
>> [1] 6
>> fact(4)
>> X is 4
>> [1] 24
>>
>>
>> 2009/4/13 Stavros Macrakis <macrakis at alum.mit.edu>:
>>> I would like to trace functions, displaying their arguments and return
>>> value, but I haven't been able to figure out how to do this with the
>>> 'trace' function.
>>>
>>> After some thrashing, I got as far as this:
>>>
>>>    fact <- function(x) if(x<1) 1 else x*fact(x-1)
>>>    tracefnc <- function() dput(as.list(parent.frame()),  #
>>> parent.frame() holds arg list
>>>                                                control=NULL)
>>>    trace("fact",tracer=tracefnc,print=FALSE)
>>>
>>> but I couldn't figure out how to access the return value of the
>>> function in the 'exit' parameter.  The above also doesn't work for
>>> "..." arguments.  (More subtly, it forces the evaluation of promises
>>> even if they are otherwise unused -- but that is, I suppose, a weird
>>> and obscure case.)
>>>
>>> Surely someone has solved this already?
>>>
>>> What I'm looking for is something very simple, along the lines of
>>> old-fashioned Lisp trace:
>>>
>>>> defun fact (i) (if (< i 1) 1 (* i (fact (+ i -1)))))
>>> FACT
>>>> (trace fact)
>>> (FACT)
>>>> (fact 3)
>>>  1> (FACT 3)
>>>    2> (FACT 2)
>>>      3> (FACT 1)
>>>        4> (FACT 0)
>>>        <4 (FACT 1)
>>>      <3 (FACT 1)
>>>    <2 (FACT 2)
>>>  <1 (FACT 6)
>>> 6
>>>
>>> Can someone help? Thanks,
>>>
>>>         -s
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>>
>>
>> --
>> HUANG Ronggui, Wincent
>> PhD Candidate
>> Dept of Public and Social Administration
>> City University of Hong Kong
>> Home page: http://asrr.r-forge.r-project.org/rghuang.html
>>
>



-- 
HUANG Ronggui, Wincent
PhD Candidate
Dept of Public and Social Administration
City University of Hong Kong
Home page: http://asrr.r-forge.r-project.org/rghuang.html