[R] Reducing the size of a large script top speed onset of execution

[Dennis Fisher]

Colleagues,

(R 2.10 on all platforms)

I have a lengthy script (18000 lines) that runs within a graphical  
interface.  The script consists of 100's of function followed by a  
single command that calls these functions (execution depends on a  
number of environment variables passed to the script).  As a result,  
nothing is executed until the final line of code is read.   It takes  
15-20 seconds to load the code - I would like to speed that process.   
Two questions:

1.  The code contains numerous large blocks that are executed under  
only one set of conditions (which are known when the code is called).   
For example, there might be code such as:
	if (CONDITION)
		{
		... (hundreds of lines of code, including embedded curly brackets)
		} else invisible()
	if (!CONDITION)
		{
		... (hundreds of lines of code, including embedded curly brackets)
		}
I assume that I could speed loading appreciably if I set up two  
scripts, each of which excluded "irrelevant" code depending on the  
CONDITION.  For example, if I knew that CONDITION was false, I would  
exclude the first block of code above; conversely, if I know that  
CONDITION was true, I would exclude the second block.

I would like to write code in R (or in sed [UNIX stream editor]) to  
create these two new scripts.  However, the regular expressions that  
would be needed are beyond me and I would appreciate help from this  
forum.  Specifically, I would like to search for:
	if (CONDITION	
or
	if (!CONDITION
as the start of the block and
	} - the matching curly bracket
at the end of the block, then remove those lines from the code.  These  
text entries are always on a line by themselves.  Finding the "if  
(CONDITION" line should be relatively easy.  The difficulty for me is  
identifying the matching curly bracket - there are often paired  
brackets within the block of code:

	if (CONDITION)
		{
		...
		if (SOMETHINGELSE)	{	}
		if (YETANOTHER)
			{
			}
		}				<-  this is the bracket that I need to match

There are also instances in which the entire block occurs on one line:
	if (CONDITION)	{ ...} else invisible()
or
	if (CONDITION ... else invisible()

Of note, I can remove the "else invisible() statements if they are  
problematic to a solution.

2.  A related issue regards loading in the graphical interface vs.  
loading at the command line (OS X).  The graphical interface loads in  
15-20 seconds - the graphical interface is sending code as rapidly as  
it can.  In contrast, at the command line, the course is source()'d  
and it takes 30-40 seconds.  I would have expected the latter approach  
to be as fast or faster because R would accept code as fast as it could.

Does anyone have an explanation for this behavior; also, any ideas as  
to how to speed the process at the command line would be appreciated.   
Thanks for any suggestions.

Dennis




Dennis Fisher MD
P < (The "P Less Than" Company)
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