On Sun, Sep 23, 2018 at 10:09 AM Wensui Liu <liuwen...@gmail.com> wrote: > > Why?
The operations required for this algorithm are vectorized, as are most operations in R. There is no need to iterate through each element. Using Vectorize to achieve the iteration is no better than using *apply or a for-loop, and betrays the same basic lack of insight into basic principles of programming in R. And/or, if you want a more practical reason: > c1 <- 1:1000000 > len <- 1000000 > system.time( s1 <- log(c1[-1]/c1[-len])) user system elapsed 0.031 0.004 0.035 > system.time(s2 <- Vectorize(function(i) log(c1[i + 1] / c1[i])) (1:len)) user system elapsed 1.258 0.022 1.282 Best, Ista > > On Sun, Sep 23, 2018 at 7:54 AM Ista Zahn <istaz...@gmail.com> wrote: >> >> On Sat, Sep 22, 2018 at 9:06 PM Wensui Liu <liuwen...@gmail.com> wrote: >> > >> > or this one: >> > >> > (Vectorize(function(i) log(c1[i + 1] / c1[i])) (1:len)) >> >> Oh dear god no. >> >> > >> > On Sat, Sep 22, 2018 at 4:16 PM rsherry8 <rsher...@comcast.net> wrote: >> > > >> > > >> > > It is my impression that good R programmers make very little use of the >> > > for statement. Please consider the following >> > > R statement: >> > > for( i in 1:(len-1) ) s[i] = log(c1[i+1]/c1[i], base = exp(1) ) >> > > One problem I have found with this statement is that s must exist before >> > > the statement is run. Can it be written without using a for >> > > loop? Would that be better? >> > > >> > > Thanks, >> > > Bob >> > > >> > > ______________________________________________ >> > > 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. >> > >> > ______________________________________________ >> > 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. ______________________________________________ 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.
