R help - Jul 2006 - RfW 2.3.1: regular expressions to detect pairs of identical word-final character sequences

Dear all

I use R for Windows 2.3.1 on a fully updated Windows XP Home SP2 machine and I
have two related regular expression problems.

platform       i386-pc-mingw32           
arch           i386                      
os             mingw32                   
system         i386, mingw32             
status                                   
major          2                         
minor          3.1                       
year           2006                      
month          06                        
day            01                        
svn rev        38247                     
language       R                         
version.string Version 2.3.1 (2006-06-01)


I would like to find cases of words in elements of character vectors that end in
the same character sequences; if I find such cases, I want to add <r> to
both potentially rhyming sequences. An example:

INPUT:This is my dog.
DESIRED OUTPUT: This<r> is<r> my dog.

I found a solution for cases where the potentially rhyming words are adjacent:

text<-"This is my dog."
gsub("(\\w+?)(\\W\\w+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)

However, with another text vector, I came across two problems I cannot seem to
solve and for which I would love to get some input.

(i) While I know what to do for non-adjacent words in general

gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", "This not is my dog",
perl=TRUE) # I know this is not proper English ;-)

this runs into problems with overlapping matches:

text<-"And this is the second sentence"
gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
[1] "And<r> this is the second<r> sentence"

It finds the "nd" match, but since the "is" match is within
the two "nd"'s, it doesn't get it. Any ideas on how to get all
pairwise matches?

(ii) How would one tell R to match only when there are 2+ characters matching?
If the above expression is applied to another character string

text<-"this is an example sentence."
gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)

it also matches the "e"'s at the end of example and sentence.
It's not possible to get rid of that by specifying a range such as {2,}

text<-"this is an example sentence."
gsub("(\\w{2,}?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)

because, as I understand it, this requires the 2+ cases of \\w to be identical
characters:

text<-"doo yoo see mee?"
gsub("(\\w{2,}?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)

Again, any ideas?

I'd really appreciate any snippets of codes, pointers, etc.
Thanks so much,
STG
--
Stefan Th. Gries
-----------------------------------------------
University of California, Santa Barbara
http://www.linguistics.ucsb.edu/faculty/stgries

The following requires more than just a single gsub but it does solve
the problem.  Modify to suit.

The first gsub places <...> around the first occurrence of any
duplicated suffixes.  We use the (?=...) zero width regexp
to circumvent the nesting problem.

Then we use strapply from the gsubfn package to extract
the suffixes so marked and paste them together to pass
to a second gsub which locates them in the original
string appending an <r> to each.   Uncomment the commented
pat if you only want to match 2+ character suffixes.

library(gsubfn)
# places <...> around first occurrences of repeated suffixes
text <- "And this is the second sentence"
pat <- "(\\w+)(?=\\b.+\\1\\b)"
# pat <- "(\\w\\w+)(?=\\b.+\\1\\b)"
out <- gsub(pat, "\\<\\1\\>", text, perl = TRUE)

suff <- strapply(out, "<([^>]+)>", function(x,y)y)[[1]]
gsub(paste("(", paste(suff, collapse = "|"),
")\\b", sep = ""), "\\1<r>", text)


On 7/22/06, Stefan Th. Gries <stgries_lists at arcor.de>
wrote:
> Dear all
>
> I use R for Windows 2.3.1 on a fully updated Windows XP Home SP2 machine
and I have two related regular expression problems.
>
> platform       i386-pc-mingw32
> arch           i386
> os             mingw32
> system         i386, mingw32
> status
> major          2
> minor          3.1
> year           2006
> month          06
> day            01
> svn rev        38247
> language       R
> version.string Version 2.3.1 (2006-06-01)
>
>
> I would like to find cases of words in elements of character vectors that
end in the same character sequences; if I find such cases, I want to add
<r> to both potentially rhyming sequences. An example:
>
> INPUT:This is my dog.
> DESIRED OUTPUT: This<r> is<r> my dog.
>
> I found a solution for cases where the potentially rhyming words are
adjacent:
>
> text<-"This is my dog."
> gsub("(\\w+?)(\\W\\w+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
>
> However, with another text vector, I came across two problems I cannot seem
to solve and for which I would love to get some input.
>
> (i) While I know what to do for non-adjacent words in general
>
> gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", "This not is my dog",
perl=TRUE) # I know this is not proper English ;-)
>
> this runs into problems with overlapping matches:
>
> text<-"And this is the second sentence"
> gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
> [1] "And<r> this is the second<r> sentence"
>
> It finds the "nd" match, but since the "is" match is
within the two "nd"'s, it doesn't get it. Any ideas on how to
get all pairwise matches?
>
> (ii) How would one tell R to match only when there are 2+ characters
matching? If the above expression is applied to another character string
>
> text<-"this is an example sentence."
> gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
>
> it also matches the "e"'s at the end of example and sentence.
It's not possible to get rid of that by specifying a range such as {2,}
>
> text<-"this is an example sentence."
> gsub("(\\w{2,}?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
>
> because, as I understand it, this requires the 2+ cases of \\w to be
identical characters:
>
> text<-"doo yoo see mee?"
> gsub("(\\w{2,}?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
>
> Again, any ideas?
>
> I'd really appreciate any snippets of codes, pointers, etc.
> Thanks so much,
> STG
> --
> Stefan Th. Gries
> -----------------------------------------------
> University of California, Santa Barbara
> http://www.linguistics.ucsb.edu/faculty/stgries
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> 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.
>

Using regular expression matching for this case may be overkill (the RE
engine will be doing a lot of backtracking looking at a lot of
non-matches).  Here is an alternative that splits the text into a vector
of words, extracts the last 2 letters of each word (remember if the last
3 letters match, then the last 2 have to match, so we only need to
consider the last 2), then looks at all pairwise comparisons for
matches, then pastes everything back together with the marked matches:

text<-"And this is a second rand  sentence"

tmp1 <- strsplit(text, ' ')[[1]]
tmp2 <- nchar(tmp1)
tmp3 <- substr(tmp1,tmp2-1,tmp2)

tmp4 <- which(lower.tri(diag(length(tmp3))), arr.ind=TRUE)
tmp5 <- tmp3[ tmp4[,1] ] == tmp3[ tmp4[,2] ]

tmp6 <- rep('', length(tmp1))
count <- 1
for( i in which(tmp5) ){
	tmp6[ tmp4[i,1] ] <- paste(tmp6[ tmp4[i,1] ],
'<r',count,'>',sep='')
	tmp6[ tmp4[i,2] ] <- paste(tmp6[ tmp4[i,2] ],
'<r',count,'>',sep='')
	count <- count + 1
}

out.text <- paste( tmp1,tmp6, sep='',collapse=' ')


If you are doing a lot of text processing like this, I would suggest
doing it in Perl rather than R.  S Poetry by Dr. Burns has a function to
take a vector of character strings in R and run a Perl script on it and
return the results.

Hope this helps,




-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111
 

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Stefan Th. Gries
Sent: Saturday, July 22, 2006 7:49 PM
To: r-help at stat.math.ethz.ch
Subject: [R] RfW 2.3.1: regular expressions to detect pairs of identical
word-final character sequences

Dear all

I use R for Windows 2.3.1 on a fully updated Windows XP Home SP2 machine
and I have two related regular expression problems.

platform       i386-pc-mingw32           
arch           i386                      
os             mingw32                   
system         i386, mingw32             
status                                   
major          2                         
minor          3.1                       
year           2006                      
month          06                        
day            01                        
svn rev        38247                     
language       R                         
version.string Version 2.3.1 (2006-06-01)


I would like to find cases of words in elements of character vectors
that end in the same character sequences; if I find such cases, I want
to add <r> to both potentially rhyming sequences. An example:

INPUT:This is my dog.
DESIRED OUTPUT: This<r> is<r> my dog.

I found a solution for cases where the potentially rhyming words are
adjacent:

text<-"This is my dog."
gsub("(\\w+?)(\\W\\w+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)

However, with another text vector, I came across two problems I cannot
seem to solve and for which I would love to get some input.

(i) While I know what to do for non-adjacent words in general

gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", "This not is my
dog", perl=TRUE) # I know this is not proper English ;-)

this runs into problems with overlapping matches:

text<-"And this is the second sentence"
gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
[1] "And<r> this is the second<r> sentence"

It finds the "nd" match, but since the "is" match is within
the two
"nd"'s, it doesn't get it. Any ideas on how to get all
pairwise matches?

(ii) How would one tell R to match only when there are 2+ characters
matching? If the above expression is applied to another character string

text<-"this is an example sentence."
gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)

it also matches the "e"'s at the end of example and sentence.
It's not
possible to get rid of that by specifying a range such as {2,}

text<-"this is an example sentence."
gsub("(\\w{2,}?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text,
perl=TRUE)

because, as I understand it, this requires the 2+ cases of \\w to be
identical characters:

text<-"doo yoo see mee?"
gsub("(\\w{2,}?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text,
perl=TRUE)

Again, any ideas?

I'd really appreciate any snippets of codes, pointers, etc.
Thanks so much,
STG
--
Stefan Th. Gries
-----------------------------------------------
University of California, Santa Barbara
http://www.linguistics.ucsb.edu/faculty/stgries

______________________________________________
R-help at stat.math.ethz.ch mailing list
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.

Before comparing times we should make sure that they functions return
the same thing.  My original function (f1 below) labels the potential
rymes with match numbers as well as finding possible rymes, if you just
want the <r> flag then the for loop can be eliminated giving f4 as
follows:

 f4 <- function(text) {
	tmp1 <- strsplit(text, ' ')[[1]]
	tmp2 <- nchar(tmp1)
	tmp3 <- substr(tmp1,tmp2-1,tmp2)

	tmp4 <- which(lower.tri(diag(length(tmp3))), arr.ind=TRUE)
	tmp5 <- tmp3[ tmp4[,1] ] == tmp3[ tmp4[,2] ]

	tmp6 <- rep('', length(tmp1))
	tmp6[ unique(c(tmp4[tmp5,])) ] <- '<r>'
	paste( tmp1,tmp6, sep='',collapse=' ') }

The speed of f4 is similar to the speed of f3 (even after correcting f3,
the original one just returns the original text string).

But that is on the sample string, what if a longer string is used (more
potential for backtracking).

Try the string generated by:

set.seed(1)
text <- paste( sample(c(letters,' ',' ',' '), 1000,
replace=T),
collapse='')
text <- gsub(" {2,}"," ",text)

Now f4 is much faster than f3.  However f3 can be optimized by replacing
\\w+ in pat by \\w{2} and that makes it faster than f4 again

It would probably be even faster to use gregexpr to just find the
matching endings then create the new regexp based on those endings and
do one substitute rather than using multiple gsubs.



-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111
 

-----Original Message-----
From: Gabor Grothendieck [mailto:ggrothendieck at gmail.com] 
Sent: Tuesday, July 25, 2006 11:41 AM
To: Greg Snow
Cc: Stefan Th. Gries; r-help at stat.math.ethz.ch
Subject: Re: [R] RfW 2.3.1: regular expressions to detect pairs of
identical word-final character sequences

Regarding having to do a lot of backtracking one can just look at the
relative comparison of speeds and we see that they are comparable in
speed.

In fact the bottleneck is not the backtacking but strapply.
I had coded the regexp version for compactness of code but if we replace
the strapply with custom gsub/strapply code for speed, the new rexexp
version is twice as fast as the for loop version.

Below f1 is the for loop version, f2 is the original regexp version with
strapply and f3 is the revised version using gsub/strsplit instead.

f1 <- function() {
	tmp1 <- strsplit(text, ' ')[[1]]
	tmp2 <- nchar(tmp1)
	tmp3 <- substr(tmp1,tmp2-1,tmp2)

	tmp4 <- which(lower.tri(diag(length(tmp3))), arr.ind=TRUE)
	tmp5 <- tmp3[ tmp4[,1] ] == tmp3[ tmp4[,2] ]

	tmp6 <- rep('', length(tmp1))
	count <- 1
	for( i in which(tmp5) ){
	       tmp6[ tmp4[i,1] ] <- paste(tmp6[ tmp4[i,1] ],
	'<r',count,'>',sep='')
	       tmp6[ tmp4[i,2] ] <- paste(tmp6[ tmp4[i,2] ],
	'<r',count,'>',sep='')
	       count <- count + 1
	}

	out.text <- paste( tmp1,tmp6, sep='',collapse=' ') }

# places <...> around first occurrences of repeated suffixes

library(gsubfn)
f2 <- function() {
	text <- "And this is the second sentence"

	pat <- "(\\w+)(?=\\b.+\\1\\b)"
	# pat <- "(\\w\\w+)(?=\\b.+\\1\\b)"
	out <- gsub(pat, "\\<\\1\\>", text, perl = TRUE)

	suff <- strapply(out, "<([^>]+)>", function(x,y)y)[[1]]
	gsub(paste("(", paste(suff, collapse = "|"),
")\\b", sep = ""),
"\\1<r>", text) }


f3 <- function() {
	text <- "And this is the second sentence"

	pat <- "(\\w+)(?=\\b.+\\1\\b)"
	# pat <- "(\\w\\w+)(?=\\b.+\\1\\b)"
	out <- gsub(pat, "\\<\\1\\>", text, perl = TRUE)

	# redo this strapply by hand for speed purposes
	# suff <- strapply(out, "<([^>]+)>", function(x,y)y)[[1]]
	suff <-
gsub("[^<>]*<|>[^<>]*<|>[^<>]*$",
"<", out)
	suff <- gsub("^<|<$", "", suff)
	suff <- strsplit(suff, "<")[[1]]
	gsub(paste("(", paste(suff, collapse = "|"),
")\\b", sep = ""),
"\\1<r>", text) }


# for loop version
system.time(for (i in 1:100) f1())  #  0.32 0.00 0.36   NA   NA

# original regexp version with strapply
system.time(for (i in 1:100) f2()) #  0.36 0.00 0.38   NA   NA

# regexp version with strapply replaced with gsub/strsplit
system.time(for (i in 1:100) f3()) # 0.15 0.00 0.16   NA   NA




On 7/25/06, Greg Snow <Greg.Snow at intermountainmail.org>
wrote:
> Using regular expression matching for this case may be overkill (the 
> RE engine will be doing a lot of backtracking looking at a lot of 
> non-matches).  Here is an alternative that splits the text into a 
> vector of words, extracts the last 2 letters of each word (remember if
> the last
> 3 letters match, then the last 2 have to match, so we only need to 
> consider the last 2), then looks at all pairwise comparisons for 
> matches, then pastes everything back together with the marked matches:
>
> text<-"And this is a second rand  sentence"
>
> tmp1 <- strsplit(text, ' ')[[1]]
> tmp2 <- nchar(tmp1)
> tmp3 <- substr(tmp1,tmp2-1,tmp2)
>
> tmp4 <- which(lower.tri(diag(length(tmp3))), arr.ind=TRUE)
> tmp5 <- tmp3[ tmp4[,1] ] == tmp3[ tmp4[,2] ]
>
> tmp6 <- rep('', length(tmp1))
> count <- 1
> for( i in which(tmp5) ){
>        tmp6[ tmp4[i,1] ] <- paste(tmp6[ tmp4[i,1] ],
> '<r',count,'>',sep='')
>        tmp6[ tmp4[i,2] ] <- paste(tmp6[ tmp4[i,2] ],
> '<r',count,'>',sep='')
>        count <- count + 1
> }
>
> out.text <- paste( tmp1,tmp6, sep='',collapse=' ')
>
>
> If you are doing a lot of text processing like this, I would suggest 
> doing it in Perl rather than R.  S Poetry by Dr. Burns has a function 
> to take a vector of character strings in R and run a Perl script on it
> and return the results.
>
> Hope this helps,
>
>
>
>
> --
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.snow at intermountainmail.org
> (801) 408-8111
>
>
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Stefan Th. 
> Gries
> Sent: Saturday, July 22, 2006 7:49 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] RfW 2.3.1: regular expressions to detect pairs of 
> identical word-final character sequences
>
> Dear all
>
> I use R for Windows 2.3.1 on a fully updated Windows XP Home SP2 
> machine and I have two related regular expression problems.
>
> platform       i386-pc-mingw32
> arch           i386
> os             mingw32
> system         i386, mingw32
> status
> major          2
> minor          3.1
> year           2006
> month          06
> day            01
> svn rev        38247
> language       R
> version.string Version 2.3.1 (2006-06-01)
>
>
> I would like to find cases of words in elements of character vectors 
> that end in the same character sequences; if I find such cases, I want
> to add <r> to both potentially rhyming sequences. An example:
>
> INPUT:This is my dog.
> DESIRED OUTPUT: This<r> is<r> my dog.
>
> I found a solution for cases where the potentially rhyming words are
> adjacent:
>
> text<-"This is my dog."
> gsub("(\\w+?)(\\W\\w+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text,
> perl=TRUE)
>
> However, with another text vector, I came across two problems I cannot
> seem to solve and for which I would love to get some input.
>
> (i) While I know what to do for non-adjacent words in general
>
> gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", "This not is my
> dog", perl=TRUE) # I know this is not proper English ;-)
>
> this runs into problems with overlapping matches:
>
> text<-"And this is the second sentence"
> gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
> [1] "And<r> this is the second<r> sentence"
>
> It finds the "nd" match, but since the "is" match is
within the two
> "nd"'s, it doesn't get it. Any ideas on how to get all
pairwise
matches?
>
> (ii) How would one tell R to match only when there are 2+ characters 
> matching? If the above expression is applied to another character 
> string
>
> text<-"this is an example sentence."
> gsub("(\\w+?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text, perl=TRUE)
>
> it also matches the "e"'s at the end of example and sentence.
It's not
> possible to get rid of that by specifying a range such as {2,}
>
> text<-"this is an example sentence."
> gsub("(\\w{2,}?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text,
> perl=TRUE)
>
> because, as I understand it, this requires the 2+ cases of \\w to be 
> identical characters:
>
> text<-"doo yoo see mee?"
> gsub("(\\w{2,}?)(\\W.+?)\\1(\\W)",
"\\1<r>\\2\\1<r>\\3", text,
> perl=TRUE)
>
> Again, any ideas?
>
> I'd really appreciate any snippets of codes, pointers, etc.
> Thanks so much,
> STG
> --
> Stefan Th. Gries
> -----------------------------------------------
> University of California, Santa Barbara 
> http://www.linguistics.ucsb.edu/faculty/stgries
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> 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 stat.math.ethz.ch mailing list
> 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.
>