R help - Sep 2009 - how to count occurrences of string?

Hi everyone,

I have an array with a variable called comments. I wish to count the number
of subjects whose post-experiment comments contain a string x and then cross
tab this with other variables of interest, ex. age. Does anyone have any
suggestions on how to count unique occurrences of a string embedded within a
variable and cross-tab it with other variables?

I've looked through the help files, etc. One method I tried was to use
strsplit to split comments. I can use this with table to count the number of
occurrences of x, but I can't cross tab this with other variables because
comments is a ragged array after being split.

Thanks in advance,

Stephen
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Here is one approach: (Some steps are intermediary steps to illustrate what
is going on)

#create sample strings
#repeat each of them 10 times

string=rep(c(
"Lorem ipsum dolor sit amet",
"Lorem ipsum, and lorem ipsum something else",
"Foo",
"Bar",
"Foobar"),10)

##Create a gender variable
gender=rep(0:1,each=25)

##Create an index variable
index=1:length(string)

##This is the string you want to look for
i.am.looking.for="Lorem ipsum"

##Return the indices of the strings 
##in which "lorem ipsum" is found?
grep(i.am.looking.for,string)

##Return a boolean for each index
##whether "lorem ipsum" is found or not?
index%in%grep(i.am.looking.for,string)

##Finally, table the occurrence/absence of
##"lorem ipsum" by gender
table(index%in%grep(i.am.looking.for,string),gender)

Hope that helps,
Daniel

-------------------------
cuncta stricte discussurus
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Gesendet: Sunday, September 20, 2009 11:58 AM
An: r-help at r-project.org
Betreff: [R] how to count occurrences of string?


Hi everyone,

I have an array with a variable called comments. I wish to count the number
of subjects whose post-experiment comments contain a string x and then cross
tab this with other variables of interest, ex. age. Does anyone have any
suggestions on how to count unique occurrences of a string embedded within a
variable and cross-tab it with other variables?

I've looked through the help files, etc. One method I tried was to use
strsplit to split comments. I can use this with table to count the number of
occurrences of x, but I can't cross tab this with other variables because
comments is a ragged array after being split.

Thanks in advance,

Stephen
--
View this message in context:
http://www.nabble.com/how-to-count-occurrences-of-string--tp25530083p2553008
3.html
Sent from the R help mailing list archive at Nabble.com.

______________________________________________
R-help at r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

This should do what you want:

set.seed(1)
# cerating a vector with comments, in which d's will be counted
comments<-character(25)
for (i in 1:25) {
   comments[i] <- paste(sample(letters[1:10], 10, replace=T),
collapse="")
}

# creating a vector to cross -tabulate
age <-sample(c("old", "young"), 25, replace=T)

# find d's in comments, determine their frequencies, and crosstab
table(sapply(gregexpr("d", comments), length), age)

HTH,
STG