search for: strcapture

I noticed a problem in the strcapture from R-devel (2016-09-27 r71386), when the text contains a missing value and perl=TRUE. { # NA in text input should map to row of NA's in output, without warning r9p <- strcapture(perl = TRUE, "(.).* ([[:digit:]]+)", c("One 1", NA, "Fifty 50"), data...

It is also not catching the cases where the number of capture expressions does not match the number of entries in proto. I think all of the following should give an error about the mismatch. > strcapture("(.)(.)", c("ab", "cde", "fgh", "ij", "lm"), proto=list(A="",B="",C="")) A B C 1 a b cd 2 d fg f 3 ij i j 4 l m ab Warning message: In matrix(as.character(unlist(str)), ncol = ntokens, byrow = TRU...

If there are any matches then strcapture can see if the pattern has the same number of capture expressions as the prototype has columns and give an error if not. That seems appropriate. If there are no matches, then there is no easy way to see if the prototype is compatible with the pattern, so should strcapture just assume the best and...

I wanted to raise the possibility of improving strcapture performance in cases where perl = TRUE. I believe we can do this in a non-breaking way by calling regexpr instead of regexec (conditionally when perl = TRUE). To illustrate this I've put together a 'proof of concept' function called strcapture2 that utilises output from regexpr directly...

Michael, thanks for looking at my first issue with utils::strcapture. Another issue is how it deals with lines that don't match the pattern. Currently it gives an error > strcapture("(.+) (.+)", c("One 1", "noSpaceInLine", "Three 3"), proto=list(Name="", Number=0)) Error in strcapture("(.+) (.+)",...

The new strcapture function in R-devel is handy, capturing the matches to the parenthesized subpatterns in a regular expression in the columns of a data.frame, whose column names and classes are given by the 'proto' argument. E.g., > p1 <- data.frame(Name="", Number=0) > str(strcapture(&q...

Hi Bill, This is a bug in regexec() and I will commit a fix. Thanks for the report, Michael On Tue, Oct 4, 2016 at 1:40 PM, William Dunlap <wdunlap at tibco.com> wrote: > I noticed a problem in the strcapture from R-devel (2016-09-27 r71386), when > the text contains a missing value and perl=TRUE. > > { > # NA in text input should map to row of NA's in output, without > warning > r9p <- strcapture(perl = TRUE, "(.).* ([[:digit:]]+)", c("One 1", NA...

...yields NAs when the pattern does not match (like strptime) and for empty captures in a matching pattern it yields the empty string, which is consistent with regmatches(). Michael On Wed, Sep 21, 2016 at 2:21 PM, William Dunlap <wdunlap at tibco.com> wrote: > If there are any matches then strcapture can see if the pattern has the same > number of capture expressions as the prototype has columns and give an > error if not. That seems appropriate. > > If there are no matches, then there is no easy way to see if the prototype > is compatible with the pattern, so should strcapture...

Hi Bill, Thanks, another good suggestion. strcapture() now returns NAs for non-matches. It's nice to have someone kicking the tires on that function. Michael On Wed, Sep 21, 2016 at 12:11 PM, William Dunlap via R-devel <r-devel at r-project.org> wrote: > Michael, thanks for looking at my first issue with utils::strcapture. > > An...

I do think keeping the default behavior is desirable for backwards compatibility; my suggestion is not to change default behavior but to add an optional argument that allows a different behavior. Although this can be implemented in a user-defined function, retaining empty matches facilitates programmatic use, and seems to be something that should be available in base R. It is available, for

Using a non-capturing group, "(?:...)" instead of "(...)", simplifies my example a bit > x <- c("Groucho <groucho at marx.com>", "<chico at marx.com>", "Harpo") > strcapture("([[:alpha:]]+)?(?: *<([[:alpha:]. ]+@[[:alpha:]. ]+)>)?", x, proto=data.frame(Name=character(), Address=character(), stringsAsFactors=FALSE)) Name Address 1 Groucho groucho at marx.com 2 chico at marx.com 3 Harpo Bill Dunlap TIBCO Software wdunlap tibco.c...

I don't care much for regmatches and haven't tried strextract, but I think replacing the character(0) by NA_character_ is almost always inappropriate if the match information comes from gregexpr. I think strcapture() does a pretty good job of what I think you are trying to do. Perhaps adding an argument to map no match to NA instead of "" would give you just what you wanted. > x <- c("Groucho <groucho at marx.com>", "<chico at marx.com>", "Harpo") &g...

I think that's a good reason for not including this in regmatches; you're right, its name is somewhat suggestive of yielding matches. Also, that sounds like a great design for strcapture with an atomic prototype. Best, CG

Thank you! I greatly appreciate your consideration, though of course it is up to you. I think many people switch to stringr/stringi simply because functions in those packages have some consistent design choices, for example, they do not drop empty/missing matches, which facilitates array-based programming. For example, in the cases where one needs to make a new column in a data.frame (data.table,

I'd be happy to entertain patches or at least more specific suggestions to improve strextract() and strcapture(). I hadn't exported strextract(), because I wasn't quite sure how it should behave. This feedback should be helpful. Thanks, Michael On Thu, Aug 29, 2019 at 2:20 PM Cyclic Group Z_1 via R-devel <r-devel at r-project.org> wrote: > > Thank you, I am aware that there are package...

...at returns a value for non-matches. Perhaps the value should be the empty string for non-matches and NA for matches to NA. The rationale is that we delegate to regexpr() (at least conceptually), and it returns a "matching region" which would be empty when there is no match. We could allow strcapture() to accept an atomic vector as a prototype, which would do what you want for regexec() (NA on no match, empty string on empty capture). Then we could call the regexpr()-based function strextract(). What do you think? Michael On Thu, Aug 29, 2019 at 3:27 PM Cyclic Group Z_1 <cyclicgroup-z1 at...

...those cases. On Mon, Sep 2, 2019 at 11:38 AM Cyclic Group Z_1 <cyclicgroup-z1 at yahoo.com> wrote: > > I think that's a good reason for not including this in regmatches; you're right, its name is somewhat suggestive of yielding matches. Also, that sounds like a great design for strcapture with an atomic prototype. > > Best, > CG -- Michael Lawrence Scientist, Bioinformatics and Computational Biology Genentech, A Member of the Roche Group Office +1 (650) 225-7760 michafla at gene.com Join Genentech on LinkedIn | Twitter | Facebook | Instagram | YouTube

Thank you, I am aware that there are packages that can accomplish this. I mentioned stringr::str_extract as a function that does not drop empty matches. I think that the behavior of regmatches(..., regexpr(...))?in base R should permit an option to prevent dropping of empty matches both for sake of consistency with the rest of the language (missing data does not yield a dropped index in other