R's { expr1; expr2; expr3} acts much like C's ( expr1, expr2, expr3) E.g.,
$ cat a.c #include <stdio.h> int main(int argc, char* argv[]) { double y = 10 ; double x = (printf("Starting... "), y = y + 100, y * 20); printf("Done: x=%g, y=%g\n", x, y); return 0; } $ gcc -Wall a.c $ ./a.out Starting... Done: x=2200, y=110 I don't like that syntax (e.g., commas between expressions instead of the usual semicolons after expressions). Perhaps John Chambers et all didn't either. -Bill On Fri, Jan 13, 2023 at 2:28 AM Valentin Petzel <valen...@petzel.at> wrote: > Hello Akshay, > > R is quite inspired by LISP, where this is a common thing. It is not in > fact that {...} returned something, rather any expression evalulates to > some value, and for a compound statement that is the last evaluated > expression. > > {...} might be seen as similar to LISPs (begin ...). > > Now this is a very different thing compared to {...} in something like C, > even if it looks or behaves similarly. But in R {...} is in fact an > expression and thus has evaluate to some value. This also comes with some > nice benefits. > > You do not need to use {...} for anything that is a single statement. But > you can in each possible place use {...} to turn multiple statements into > one. > > Now think about a statement like this > > f <- function(n) { > x <- runif(n) > x**2 > } > > Then we can do > > y <- f(10) > > Now, you suggested way would look like this: > > f <- function(n) { > x <- runif(n) > y <- x**2 > } > > And we'd need to do something like: > > f(10) > y <- somehow_get_last_env_of_f$y > > So having a compound statement evaluate to a value clearly has a benefit. > > Best Regards, > Valentin > > 09.01.2023 18:05:58 akshay kulkarni <akshay...@hotmail.com>: > > > Dear Valentin, > > But why should {....} "return" a value? It > could just as well evaluate all the expressions and store the resulting > objects in whatever environment the interpreter chooses, and then it would > be left to the user to manipulate any object he chooses. Don't you think > returning the last, or any value, is redundant? We are living in the > 21st century world, and the R-core team might,I suppose, have a definite > reason for"returning" the last value. Any comments? > > > > Thanking you, > > Yours sincerely, > > AKSHAY M KULKARNI > > > > ---------------------------------------- > > *From:* Valentin Petzel <valen...@petzel.at> > > *Sent:* Monday, January 9, 2023 9:18 PM > > *To:* akshay kulkarni <akshay...@hotmail.com> > > *Cc:* R help Mailing list <r-help@r-project.org> > > *Subject:* Re: [R] return value of {....} > > > > Hello Akshai, > > > > I think you are confusing {...} with local({...}). This one will > evaluate the expression in a separate environment, returning the last > expression. > > > > {...} simply evaluates multiple expressions as one and returns the > result of the last line, but it still evaluates each expression. > > > > Assignment returns the assigned value, so we can chain assignments like > this > > > > a <- 1 + (b <- 2) > > > > conveniently. > > > > So when is {...} useful? Well, anyplace where you want to execute > complex stuff in a function argument. E.g. you might do: > > > > data %>% group_by(x) %>% summarise(y = {if(x[1] > 10) sum(y) else > mean(y)}) > > > > Regards, > > Valentin Petzel > > > > 09.01.2023 15:47:53 akshay kulkarni <akshay...@hotmail.com>: > > > >> Dear members, > >> I have the following code: > >> > >>> TB <- {x <- 3;y <- 5} > >>> TB > >> [1] 5 > >> > >> It is consistent with the documentation: For {, the result of the last > expression evaluated. This has the visibility of the last evaluation. > >> > >> But both x AND y are created, but the "return value" is y. How can this > be advantageous for solving practical problems? Specifically, consider the > following code: > >> > >> F <- function(X) { expr; expr2; { expr5; expr7}; expr8;expr10} > >> > >> Both expr5 and expr7 are created, and are accessible by the code > outside of the nested braces right? But the "return value" of the nested > braces is expr7. So doesn't this mean that only expr7 should be accessible? > Please help me entangle this (of course the return value of F is expr10, > and all the other objects created by the preceding expressions are deleted. > But expr5 is not, after the control passes outside of the nested braces!) > >> > >> Thanking you, > >> Yours sincerely, > >> AKSHAY M KULKARNI > >> > >> [[alternative HTML version deleted]] > >> > >> ______________________________________________ > >> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >> 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. > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.