Thanks. Very informative. I certainly missed this. -- Bert
On Sat, Dec 3, 2022 at 3:49 PM Hervé Pagès <hpages.on.git...@gmail.com> wrote: > On 03/12/2022 07:21, Bert Gunter wrote: > > Perhaps it is worth pointing out that looping constructs like lapply() > can > > be avoided and the procedure vectorized by mimicking Martin Morgan's > > solution: > > > > ## s is the string to be searched. > > diff(c(0,grep('b',strsplit(s,'')[[1]]))) > > > > However, Martin's solution is simpler and likely even faster as the regex > > engine is unneeded: > > > > diff(c(0, which(strsplit(s, "")[[1]] == "b"))) ## completely vectorized > > > > This seems much preferable to me. > > Of all the proposed solutions, Andrew Hart's solution seems the most > efficient: > > big_string <- strrep("abaaabbaaaaabaaabaaaaaaaaaaaaaaaaaaab", 500000) > > system.time(nchar(strsplit(big_string, split="b", fixed=TRUE)[[1]]) + 1) > # user system elapsed > # 0.736 0.028 0.764 > > system.time(diff(c(0, which(strsplit(big_string, "", fixed=TRUE)[[1]] > == "b")))) > # user system elapsed > # 2.100 0.356 2.455 > > The bigger the string, the bigger the gap in performance. > > Also, the bigger the average gap between 2 successive b's, the bigger > the gap in performance. > > Finally: always use fixed=TRUE in strsplit() if you don't need to use > the regex engine. > > Cheers, > > H. > > > > -- Bert > > > > > > > > > > > > On Sat, Dec 3, 2022 at 12:49 AM Rui Barradas <ruipbarra...@sapo.pt> > wrote: > > > >> Às 17:18 de 02/12/2022, Evan Cooch escreveu: > >>> Was wondering if there is an 'efficient/elegant' way to do the > following > >>> (without tidyverse). Take a string > >>> > >>> abaaabbaaaaabaaab > >>> > >>> Its easy enough to count the number of times the character 'b' shows up > >>> in the string, but...what I'm looking for is outputing the 'intervals' > >>> between occurrences of 'b' (starting the counter at the beginning of > the > >>> string). So, for the preceding example, 'b' shows up in positions > >>> > >>> 2, 6, 7, 13, 17 > >>> > >>> So, the interval data would be: 2, 4, 1, 6, 4 > >>> > >>> My main approach has been to simply output positions (say, something > >>> like unlist(gregexpr('b', target_string))), and 'do the math' between > >>> successive positions. Can anyone suggest a more elegant approach? > >>> > >>> Thanks in advance... > >>> > >>> ______________________________________________ > >>> 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. > >> Hello, > >> > >> I don't find your solution inelegant, it's even easy to write it as a > >> one-line function. > >> > >> > >> char_interval <- function(x, s) { > >> lapply(gregexpr(x, s), \(y) c(head(y, 1), diff(y))) > >> } > >> > >> target_string <-"abaaabbaaaaabaaab" > >> char_interval('b', target_string) > >> #> [[1]] > >> #> [1] 2 4 1 6 4 > >> > >> > >> Hope this helps, > >> > >> Rui Barradas > >> > >> ______________________________________________ > >> 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. > > -- > Hervé Pagès > > Bioconductor Core Team > hpages.on.git...@gmail.com > > [[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.