[R] element wise pattern recognition and string substitution

Jun Shen jun.shen.ut at gmail.com
Wed Sep 7 05:59:12 CEST 2016 

Hi Ista,

Thanks for the suggestion. I didn't know mapply can be used this way! Let
me take one more step. Instead of defining a pattern for each string, I
would like to define a set of patterns from all the possible combination of
the unique values of those variables. Then I need each string to find a
pattern for itself. I know this is getting a little stretching. Thanks for
all the suggestion/comments from everyone.

Jun

On Tue, Sep 6, 2016 at 9:44 PM, Ista Zahn <istazahn at gmail.com> wrote:

> If you want to mach each element of 'strings' to a different regex, do
> it. Here are three ways, using your original example.
>
> pattern1 <- "([^.]*)\\.([^.]*\\.[^.]*)\\.(.*)"
> pattern2 <- "([^.]*)\\.([^.]*)\\.(.*)"
>
> patterns <- c(pattern1,pattern2)
> strings <- c('TX.WT.CUT.mean','mg.tx.cv')
>
> for(i in seq(strings)) print(sub(patterns[i], "\\2", strings[i]))
>
> mapply(sub, pattern = patterns, x = strings, MoreArgs=list(replacement =
> "\\2"))
>
> library(stringi)
> stri_replace_all_regex(strings, patterns, "$2")
>
> Best,
> Ista
> On Tue, Sep 6, 2016 at 9:20 PM, Jun Shen <jun.shen.ut at gmail.com> wrote:
> > Hi Jeff,
> >
> > Thanks for the reply. I tried your suggestion and it doesn't seem to work
> > and I tried a simple pattern as follows and it works as expected
> >
> > sub("(3\\.mg\\.kg)\\.(>50-70\\.kg)\\.(.*)", '\\1', "3.mg.kg
> .>50-70.kg.P05")
> > [1] "3.mg.kg"
> >
> > sub("(3\\.mg\\.kg)\\.(>50-70\\.kg)\\.(.*)", '\\2', "3.mg.kg
> .>50-70.kg.P05")
> > [1] ">50-70.kg"
> >
> > sub("(3\\.mg\\.kg)\\.(>50-70\\.kg)\\.(.*)", '\\3', "3.mg.kg
> .>50-70.kg.P05")
> > [1] "P05"
> >
> > My problem is the pattern has to be dynamically constructed on the input
> > data of the function I am writing. It's actually not too difficult to
> > assemble the final.pattern with some code like the following
> >
> > sort.var <- c('TX','WTCUT')
> > combn.sort.var <- do.call(expand.grid, lapply(sort.var,
> > function(x)paste('(',gsub('\\.','\\\\.',unlist(unique(all.
> exposure[x]))),
> > ')', sep='')))
> > all.patterns <- do.call(paste, c(combn.sort.var, '(.*)', sep='\\.'))
> > final.pattern <- paste0(all.patterns, collapse='|')
> >
> > You cannot run the code directly since the data object "all.exposure" is
> > not provided here.
> >
> > Jun
> >
> >
> >
> > On Tue, Sep 6, 2016 at 8:18 PM, Jeff Newmiller <jdnewmil at dcn.davis.ca.us
> >
> > wrote:
> >
> >> I am not near my computer today, but each parenthesis gets its own
> result
> >> number, so you should put the parenthesis around the whole pattern of
> >> alternatives instead of having many parentheses.
> >>
> >> I recommend thinking in terms of what common information you expect to
> >> find in these various strings, and place your parentheses to capture
> that
> >> information. There is no other reason to put parentheses in the
> pattern...
> >> they are not grouping symbols.
> >> --
> >> Sent from my phone. Please excuse my brevity.
> >>
> >> On September 6, 2016 5:01:04 PM PDT, Bert Gunter <
> bgunter.4567 at gmail.com>
> >> wrote:
> >> >Jun:
> >> >
> >> >1. Tell us your desired result from your test vector and maybe someone
> >> >will help.
> >> >
> >> >2. As we played this game once already (you couldn't do it; I showed
> >> >you how), this seems to be a function of your limitations with regular
> >> >expressions. I'm probably not much better, but in any case, I don't
> >> >intend to be your consultant. See if you can find someone locally to
> >> >help you if you do not receive a satisfactory reply from the list.
> >> >There are many people here who are pretty good at this sort of thing,
> >> >but I don't know if they'll reply. Regex's are certainly complex. PERL
> >> >people tend to be pretty good at them, I believe. There are numerous
> >> >web sites and books on them if you need to acquire expertise for your
> >> >work.
> >> >
> >> >Cheers,
> >> >Bert
> >> >Bert Gunter
> >> >
> >> >"The trouble with having an open mind is that people keep coming along
> >> >and sticking things into it."
> >> >-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
> >> >
> >> >
> >> >On Tue, Sep 6, 2016 at 3:59 PM, Jun Shen <jun.shen.ut at gmail.com>
> wrote:
> >> >> Hi Bert,
> >> >>
> >> >> I still couldn't make the multiple patterns to work. Here is an
> >> >example. I
> >> >> make the pattern as follows
> >> >>
> >> >> final.pattern <-
> >> >>
> >> >"(240\\.m\\.g)\\.(>50-70\\.kg)\\.(.*)|(3\\.mg\\.kg)\\.(>
> >> 50-70\\.kg)\\.(.*)|(240\\.m\\.g)\\.(>70-90\\.kg)\\.(.*)|(3\\
> >> .mg\\.kg)\\.(>70-90\\.kg)\\.(.*)|(240\\.m\\.g)\\.(>90-110\\.
> >> kg)\\.(.*)|(3\\.mg\\.kg)\\.(>90-110\\.kg)\\.(.*)|(240\\.m\\
> >> .g)\\.(50\\.kg\\.or\\.less)\\.(.*)|(3\\.mg\\.kg)\\.(50\\.kg\
> >> \.or\\.less)\\.(.*)|(240\\.m\\.g)\\.(>110\\.kg)\\.(.*)|(3\\.
> >> mg\\.kg)\\.(>110\\.kg)\\.(.*)"
> >> >>
> >> >> test.string <- c('240.m.g.>110.kg.geo.mean', '3.mg.kg.>110.kg.P05',
> >> >> '240.m.g.>50-70.kg.geo.mean')
> >> >>
> >> >> sub(final.pattern, '\\1', test.string)
> >> >> sub(final.pattern, '\\2', test.string)
> >> >> sub(final.pattern, '\\3', test.string)
> >> >>
> >> >> Only the third string has been correctly parsed, which matches the
> >> >first
> >> >> pattern. It seems the rest of the patterns are not called.
> >> >>
> >> >> Jun
> >> >>
> >> >>
> >> >> On Mon, Sep 5, 2016 at 10:21 PM, Bert Gunter <bgunter.4567 at gmail.com
> >
> >> >wrote:
> >> >>>
> >> >>> Just noticed: My clumsy do.call() line in my previously posted code
> >> >>> below should be replaced with:
> >> >>> pat <- paste(pat,collapse = "|")
> >> >>>
> >> >>>
> >> >>> > pat <- c(pat1,pat2)
> >> >>> > paste(pat,collapse="|")
> >> >>> [1] "a+\\.*a+|b+\\.*b+"
> >> >>>
> >> >>> ************ replace this **************************
> >> >>> > pat <- do.call(paste,c(as.list(pat), sep="|"))
> >> >>> ********************************************
> >> >>> > sub(paste0("^[^b]*(",pat,").*$"),"\\1",z)
> >> >>> [1] "a.a"   "bb"    "b.bbb"
> >> >>>
> >> >>>
> >> >>> -- Bert
> >> >>> Bert Gunter
> >> >>>
> >> >>> "The trouble with having an open mind is that people keep coming
> >> >along
> >> >>> and sticking things into it."
> >> >>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
> >> >>>
> >> >>>
> >> >>> On Mon, Sep 5, 2016 at 12:11 PM, Bert Gunter
> >> ><bgunter.4567 at gmail.com>
> >> >>> wrote:
> >> >>> > Jun:
> >> >>> >
> >> >>> > You need to provide a clear specification via regular expressions
> >> >of
> >> >>> > the patterns you wish to match -- at least for me to decipher it.
> >> >>> > Others may be smarter than I, though...
> >> >>> >
> >> >>> > Jeff: Thanks. I have now convinced myself that it can be done (a
> >> >>> > "proof" of sorts): If pat1, pat2,..., patn are m different
> >> >patterns
> >> >>> > (in a vector of patterns)  to be matched in a vector of n strings,
> >> >>> > where only one of the patterns will match in any string,  then use
> >> >>> > paste() (probably via do.call()) or otherwise to paste them
> >> >together
> >> >>> > separated by "|" to form the concatenated pattern, pat. Then
> >> >>> >
> >> >>> > sub(paste0("^.*(",pat, ").*$"),"\\1",thevector)
> >> >>> >
> >> >>> > should extract the matching pattern in each (perhaps with a little
> >> >>> > fiddling due to precedence rules); e.g.
> >> >>> >
> >> >>> >> z <-c(".fg.h.g.a.a", "bb..dd.ef.tgf.", "foo...b.bbb.tgy")
> >> >>> >
> >> >>> >> pat1 <- "a+\\.*a+"
> >> >>> >> pat2 <-"b+\\.*b+"
> >> >>> >> pat <- c(pat1,pat2)
> >> >>> >
> >> >>> >> pat <- do.call(paste,c(as.list(pat), sep="|"))
> >> >>> >> pat
> >> >>> > [1] "a+\\.*a+|b+\\.*b+"
> >> >>> >
> >> >>> >> sub(paste0("^[^b]*(",pat,").*$"), "\\1", z)
> >> >>> > [1] "a.a"   "bb"    "b.bbb"
> >> >>> >
> >> >>> > Cheers,
> >> >>> > Bert
> >> >>> >
> >> >>> >
> >> >>> > Bert Gunter
> >> >>> >
> >> >>> > "The trouble with having an open mind is that people keep coming
> >> >along
> >> >>> > and sticking things into it."
> >> >>> > -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
> >> >>> >
> >> >>> >
> >> >>> > On Mon, Sep 5, 2016 at 9:56 AM, Jun Shen <jun.shen.ut at gmail.com>
> >> >wrote:
> >> >>> >> Thanks for the reply, Bert.
> >> >>> >>
> >> >>> >> Your solution solves the example. I actually have a more general
> >> >>> >> situation
> >> >>> >> where I have this dot concatenated string from multiple
> >> >variables. The
> >> >>> >> problem is those variables may have values with dots in there.
> >> >The
> >> >>> >> number of
> >> >>> >> dots are not consistent for all values of a variable. So I am
> >> >thinking
> >> >>> >> to
> >> >>> >> define a vector of patterns for the vector of the string and
> >> >hopefully
> >> >>> >> to
> >> >>> >> find a way to use a pattern from the pattern vector for each
> >> >value of
> >> >>> >> the
> >> >>> >> string vector. The only way I can think of is "for" loop, which
> >> >can be
> >> >>> >> slow.
> >> >>> >> Also these are happening in a function I am writing. Just wonder
> >> >if
> >> >>> >> there is
> >> >>> >> another more efficient way. Thanks a lot.
> >> >>> >>
> >> >>> >> Jun
> >> >>> >>
> >> >>> >> On Mon, Sep 5, 2016 at 1:41 AM, Bert Gunter
> >> ><bgunter.4567 at gmail.com>
> >> >>> >> wrote:
> >> >>> >>>
> >> >>> >>> Well, he did provide an example, and...
> >> >>> >>>
> >> >>> >>>
> >> >>> >>> > z <- c('TX.WT.CUT.mean','mg.tx.cv')
> >> >>> >>>
> >> >>> >>> > sub("^.+?\\.(.+)\\.[^.]+$","\\1",z)
> >> >>> >>> [1] "WT.CUT" "tx"
> >> >>> >>>
> >> >>> >>>
> >> >>> >>> ## seems to do what was requested.
> >> >>> >>>
> >> >>> >>> Jeff would have to amplify on his initial statement however: do
> >> >you
> >> >>> >>> mean that separate patterns can always be combined via "|" ?  Or
> >> >>> >>> something deeper?
> >> >>> >>>
> >> >>> >>> Cheers,
> >> >>> >>> Bert
> >> >>> >>> Bert Gunter
> >> >>> >>>
> >> >>> >>> "The trouble with having an open mind is that people keep coming
> >> >along
> >> >>> >>> and sticking things into it."
> >> >>> >>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip
> >> >)
> >> >>> >>>
> >> >>> >>>
> >> >>> >>> On Sun, Sep 4, 2016 at 9:30 PM, Jeff Newmiller
> >> >>> >>> <jdnewmil at dcn.davis.ca.us>
> >> >>> >>> wrote:
> >> >>> >>> > Your opening assertion is false.
> >> >>> >>> >
> >> >>> >>> > Provide a reproducible example and someone will demonstrate.
> >> >>> >>> > --
> >> >>> >>> > Sent from my phone. Please excuse my brevity.
> >> >>> >>> >
> >> >>> >>> > On September 4, 2016 9:06:59 PM PDT, Jun Shen
> >> >>> >>> > <jun.shen.ut at gmail.com>
> >> >>> >>> > wrote:
> >> >>> >>> >>Dear list,
> >> >>> >>> >>
> >> >>> >>> >>I have a vector of strings that cannot be described by one
> >> >pattern.
> >> >>> >>> >> So
> >> >>> >>> >>let's say I construct a vector of patterns in the same length
> >> >as the
> >> >>> >>> >>vector
> >> >>> >>> >>of strings, can I do the element wise pattern recognition and
> >> >string
> >> >>> >>> >>substitution.
> >> >>> >>> >>
> >> >>> >>> >>For example,
> >> >>> >>> >>
> >> >>> >>> >>pattern1 <- "([^.]*)\\.([^.]*\\.[^.]*)\\.(.*)"
> >> >>> >>> >>pattern2 <- "([^.]*)\\.([^.]*)\\.(.*)"
> >> >>> >>> >>
> >> >>> >>> >>patterns <- c(pattern1,pattern2)
> >> >>> >>> >>strings <- c('TX.WT.CUT.mean','mg.tx.cv')
> >> >>> >>> >>
> >> >>> >>> >>Say I want to extract "WT.CUT" from the first string and "tx"
> >> >from
> >> >>> >>> >> the
> >> >>> >>> >>second string. If I do
> >> >>> >>> >>
> >> >>> >>> >>sub(patterns, '\\2', strings), only the first pattern will be
> >> >used.
> >> >>> >>> >>
> >> >>> >>> >>looping the patterns doesn't work the way I want. Appreciate
> >> >any
> >> >>> >>> >>comments.
> >> >>> >>> >>Thanks.
> >> >>> >>> >>
> >> >>> >>> >>Jun
> >> >>> >>> >>
> >> >>> >>> >>       [[alternative HTML version deleted]]
> >> >>> >>> >>
> >> >>> >>> >>______________________________________________
> >> >>> >>> >>R-help at 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 at 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 at 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.
>

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