R help - Oct 2007 - tricky problem with "if" function -

Hi all,

This question involves using a "for" loop to make a
"decision" in a script.

I've written a rather intricate script, and near the start of it, I
want it either to do a loop (if a variable called "number.runs" >
1)
or not do a loop (if "number.runs" is 1). This is probably trivial but
I can't figure it out. Here's a self-contained example that gets at
the gist of what I'm looking for:

number.runs <- 1   #try it with number.runs <- 2 as well
if (number.runs==1) run.number <- 1
if (number.runs>1) for(run.number in 1:number.runs){
print(number.runs)   #in the real script, lots happens in here
if(number.runs>1) }

I'd like the following to print "1" if number.runs==1, and print
"1"
and then "2" if number.runs==2.

But the above syntax does not work. R returns a Syntax Error. This
probably has to do with the order of operations?

Then I thought I would get tricky and use an eval(parse()) statement:

if (number.runs==1) cat("run.number <- 1",file="temp")
if (number.runs>1)  cat("for(run.number in
1:number.runs){",file="temp")
eval(parse(file="temp"))
print(number.runs)   #in the real script, lots happens in here
if(number.runs>1) cat("}",file="temp")
eval(parse(file="temp"))

But R returns the following error:

Error in parse(file, n, text, prompt, srcfile, encoding) :
	temp: syntax error, unexpected END_OF_INPUT, expecting '\n' or
';' or '}' at
2: for(run.number in 1:number.runs){


-- 
Matthew C Keller
Postdoctoral Fellow
Virginia Institute for Psychiatric and Behavioral Genetics

This is confusing.

try this.

number.runs <- 1
if (number.runs == 1) run.number <- 1
if (number.runs > 1) {
  for (i in 1:number.runs) {
    print(i)
  }
}

perhaps the easiest way to print 1 and then 1 2 would be

for (i in 1:number.runs) {
  print(i)
}

but i'm not sure that is what you want.

i'm also not sure what the if(number.runs>1) is doing inside your for
loop -- the for loop is only executed under that condition.


On 10/2/07, Matthew Keller <mckellercran at gmail.com>
wrote:
> Hi all,
>
> This question involves using a "for" loop to make a
"decision" in a script.
>
> I've written a rather intricate script, and near the start of it, I
> want it either to do a loop (if a variable called "number.runs"
> 1)
> or not do a loop (if "number.runs" is 1). This is probably
trivial but
> I can't figure it out. Here's a self-contained example that gets at
> the gist of what I'm looking for:
>
> number.runs <- 1   #try it with number.runs <- 2 as well
> if (number.runs==1) run.number <- 1
> if (number.runs>1) for(run.number in 1:number.runs){
> print(number.runs)   #in the real script, lots happens in here
> if(number.runs>1) }
>
> I'd like the following to print "1" if number.runs==1, and
print "1"
> and then "2" if number.runs==2.
>
> But the above syntax does not work. R returns a Syntax Error. This
> probably has to do with the order of operations?
>
> Then I thought I would get tricky and use an eval(parse()) statement:
>
> if (number.runs==1) cat("run.number <-
1",file="temp")
> if (number.runs>1)  cat("for(run.number in
1:number.runs){",file="temp")
> eval(parse(file="temp"))
> print(number.runs)   #in the real script, lots happens in here
> if(number.runs>1) cat("}",file="temp")
> eval(parse(file="temp"))
>
> But R returns the following error:
>
> Error in parse(file, n, text, prompt, srcfile, encoding) :
>         temp: syntax error, unexpected END_OF_INPUT, expecting '\n'
or ';' or '}' at
> 2: for(run.number in 1:number.runs){
>
>
> --
> Matthew C Keller
> Postdoctoral Fellow
> Virginia Institute for Psychiatric and Behavioral Genetics
>
> ______________________________________________
> 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.
>

-- 
Tim Calkins
0406 753 997