"McGehee, Robert" <[EMAIL PROTECTED]> writes: > Greetings, > I'm having some difficulties with evaluating very long expressions > (Windows/Linux 2.0.1), as seen below, and would greatly appreciate any > help, thoughts or work arounds. Let's say that I wanted to see what I > would get if I added 1 to itself 498 times. One way of doing this would > be to evaluate the expression 1+1+1+... > > > eval(parse(text = paste(rep(1, 498), collapse = "+"))) > [1] 498 > > However, if we try this with 499+ items we get no answer: > > a <- eval(parse(text = paste(rep(1, 499), collapse = "+"))) > > a > Error: Object "a" not found > > And if this eval is passed to any other function, that function exits > without error and without returning and object. > > So it seems that we've reached some upper limit of evaluation terms. > While the parser is able to correctly create the long expression, eval > does not successfully evaluate it. > My problem is that since the evaluator does not return an object, error, > or warning, I'm not able to easily code around this problem. Also, I've > thought of no easy way to "count" the terms in the expression to see > whether we've breached the upper limit or not.
It's a bug. 1.9.1 had > eval(parse(text = paste(rep(1, 499), collapse = "+"))) Error in eval(expr, envir, enclos) : evaluation nested too deeply: infinite recursion / options(expression=)? which also contains the hint about how to raise the limit. You do see it if you do > a <- try(eval(parse(text = paste(rep(1, 499), collapse = "+")))) > a [1] "evaluation nested too deeply: infinite recursion / options(expression=)?" attr(,"class") [1] "try-error" but that's obviously no excuse for not printing the message. The problem appears still to be present in r-devel (the version at hand was dated Jan.12, though). > If I were able to see if the eval would work on a particular expression, > one thing I had considered was to make an eval.long wrapper that peels > terms off the right hand side of an overly-long expression until every > sub-expression is legal. But do you *really* want to do it this way? Why? BTW, it's not really the length of the expression but its depth. The parse tree for 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 is really (((((((1+2)+3)+4)+5)+6)+7)+8). So you get 7 levels of parentheses. You can easily have less deeply nested parentheses: ((1+2)+(3+4))+((5+6)+(7+8)) With that sort of pattern, adding 500 terms requires a nesting no more than 9 levels deep. Persuading R to nest that way is a bit tricky though. -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-devel@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
