[R] Conditionally skip over "for(..){" and "}"??

[jim holtman]

A safer way is:

for (i in seq_along(VarNames)){
....

What happens when VarNames is length zero:

> x <- NULL
> 1:length(x)
[1] 1 0
> seq_along(x)
integer(0)
>


On Sun, Oct 12, 2008 at 11:00 AM, Ted Harding
<Ted.Harding at manchester.ac.uk> wrote:
> Following up on Barry's suggestion led on to a more straightforward
> approach:
>
>  VarNames <- NULL
> # VarNames <- c(VarNames, "Var1")
> # VarNames <- c(VarNames, "Var2")
> # VarNames <- c(VarNames, "Var3")
> # [...]
>  for(i in (1:length(VarNames))){
>    VarName <- VarNames[i]
>    [...]
>
> Then any one or some of those lines can be uncommented.
>
> With thanks for the suggestions.
> Ted.
>
> On 12-Oct-08 11:32:31, Barry Rowlingson wrote:
>> 2008/10/12 Ted Harding <Ted.Harding at manchester.ac.uk>:
>>> Hi Folks,
>>> I'm wondering if there's a secret trick to achieve the following.
>>>
>>> I have some big code for analysis related to a named variable,
>>> which will be one of several in the columns of a dataframe, and
>>> I would like to be able to choose between a run for just one of
>>> these variables, or a run which loops over them all.
>>>
>>> So, for a single run, I could have the following kind of thing
>>> in a file code.R to be sourced by source("code.R"):
>>>
>>> # VarName <- "Var1"
>>>  VarName <- "Var2"
>>> # VarName <- "Var3"
>>> # VarName <- "Var4"
>>>
>>> ### CUT OUT LOOP
>>> # VarNames <- c("Var1","Var2","Var3","Var4")
>>> # for( VarName in VarNames ) {
>>>
>>> << Lots of code related to analysis of variable VarName >>
>>>
>>> ### CUT OUT END OF LOOP
>>> # }
>>>
>>> which would do the single case for Var2. A run for a different VarName
>>> would be done by editing the first block to select the new VarName.
>>>
>>> Now, when I want to run the loop over all VarNames, I could of course
>>> likewise edit the file so as to uncomment the code which follows the
>>> "CUT OUT ..." lines. But I would prefer to avoid having to do the
>>> latter, and am therefore wondering if there is some way to
>>> conditionally
>>> skip over those bits of code.
>>
>>  What's the problem with doing a loop over a single VarName in
>> VarNames? I'd put something like:
>>
>>  VarNames = c(
>> "Var1",
>> "Var2",
>> "Var3"
>> )
>>
>>  at the start of my code for easy editing, and then if I only wanted
>> to do it for one VarName you can just do:
>>
>> VarNames = c(
>>#"Var1",
>> "Var2"
>>#"Var3"
>> )
>>
>>  - it's just a shame that R doesn't like trailing commas in c() calls,
>> which would make it even easier.
>>
>>  Of course the real way to do it is to rewrite it as a function and do
>> foo(c("Var1","Var2")) as desired....
>>
>> Barry
>>
>> ______________________________________________
>> 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.
>
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
> Fax-to-email: +44 (0)870 094 0861
> Date: 12-Oct-08                                       Time: 16:00:14
> ------------------------------ XFMail ------------------------------
>
> ______________________________________________
> 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.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?