Naresh, > I want to source some data from databases, then use this data in > various blocks. I am looking for the most efficient way to achieve > this. In below blocks, is the code in block ``connection'' executed > thrice (economy of code but no saving of time) or is it only executed > once then used twice? If the code is run thrice, is there another way > to create code blocks so that the code is executed only once?
if you export this "file", the "connection" block will execute three times. Vikas suggested a session, which is something i often do for interactive work. or, the R code in "connection" could also use R variables to protect itself against multiple executions. or, i suppose you could invoke "connection" via a :var variable (rather than via =<<connection>>), and use the :cache keyword to restrict connection's evaluation to "every now and then" (for a very precisely-defined, if not always intuitively definition of "every now and then"). you'd have to be careful to not get bitten by the code *not* being evaluated, and by it being evaluated too often. (probably too clever by half.) hth, cheers, Greg
