[R] How to modify the body of a function?

[William Dunlap]

The problem with Don's
  if (condition) {
      Results <- something
  } else {
      Results <- somethingElse
  }
is that in a long sequence of if-then-else-if... you have
to check every branch to make sure Results got assigned to
(or that the remaining branches contained a return() or a stop()).

Duncan's version may be more readable if you explicitly assign
the value of the if-then-else to a variable and then return the variable
  Results <- if (condition) {
                       something
                   } else {
                        somethingElse
                   }
  Return

I think the original poster may have wanted to put a trace on a function
that could display the return value of the function, for an arbitrary function.
Having a return() statement makes this more difficult, since you
cannot simply make a transformation from
   origFun <- function(...) body
to
   newFun <- function(...) { retVal <- body ; print(retVal) ; retVal }
I think you really have to make a new function that wraps the original one, like
   newFun <- function(...) { retVal <- origFun(...) ; print(retVal) ; retval }
The latter will not work with functions that that use things like
sys.parent() so you may have to go into the body of the code and patch
those up.

(My preferences are colored by my experience looking for problems in
other people's code.  My own code is always easy to understand but
code other people write can be difficult. :-))


Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Sun, Jul 27, 2014 at 5:14 PM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> On 27/07/2014, 7:29 PM, MacQueen, Don wrote:
>> As long as people are sharing their preferences . . .
>>
>>
>> I find return() useful in a scenario like the following:
>>
>> Myfun <- function() {
>>   {a few lines of code}
>>   if (condition) return(whatever)
>>   {Many, many lines of code}
>>   Results
>> }
>>
>> Which I find preferable to
>>
>> Myfun <- function() {
>>   { a few lines of code}
>>   if (condition) {
>>     Results <- something
>>   } else {
>>     {Many, many lines of code}
>>     Results <- something.else
>>   }
>>   Results
>> }
>>
>
> I tend to agree with you, but wanted to point out a third possibility:
>
>
>  Myfun <- function() {
>    { a few lines of code}
>    if (condition) {
>      something
>    } else {
>      {Many, many lines of code}
>      something.else
>    }
> }
>
> In some sense this is the most "R-like", but I like it the least.
>
> Duncan Murdoch
>>
>> It is the presence of those many lines of code which separate the opening
>> and closing brackets after the else that make the former easier to read
>> and understand (again in my opinion).
>>
>> I guess this is more along the lines of exception handling.
>>
>> Also note that this is something of a special case; I don¹t in general
>> advocate using return().
>>
>
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