[R] Performance of concatenating strings

[Tamara Steijger]

Hi,
thanks for the fast answers. I'm sorry, if I was not clear enough in  
my question. The problem we are trying to solve is LetterDisplay.  
There is already a heuristic implemented in the multcompView package  
of Hans-Peter Piepho. We implemented an exact fixed parameter  
tractable implementation for that problem (implementation in OCaml).

The new R function works similar like the original multcompLetters  
function. But instead of running the heuristic the input is forwarded  
to the OCaml program. Because the new multcompView function should  
have the same return format as the original one (users don't have to  
bother about the new implementation and still use the old code) the  
output then has to be formatted in the same way as it is done by now  
in multcompLetters.

The output of the OCaml program is a file containing a matrix. Names  
that occur in the same row of the matrix are not significant  
different, so they should have a common letter in the LetterDisplay,  
i.e. each row in the matrix corresponds to one letter in the  
LetterDisplay. Right now those LetterDisplays are build up character  
by character like it was in the original function. But as you already  
mentioned storing for each name the characters as a list (i.e. a  
matrix with a row for each name and so many columns as lines in the  
output file) and then concatenating all at once probably will improve  
the performance already significantly. And runtime is in this case  
probably more critical than memory issues.

I didn't use Rprof so far, but I will definitely try it. But just to  
get an idea of what the problem is: The input for a LetterDisplay can  
also be given as a graph. One of our test instances is a graph with  
121 nodes and 5108 edges. The OCaml program needs ca. 1 second to  
compute the result. But then computing the LetterDisplays needs more  
than two hours ...

Thanks a lot,
T. Steijger