使用正则表达式从文件中提取文本的一部分

Question

I am trying to use the following code:

x <- scan("myfile.txt", what="", sep="\n")

b <- grep('/^one/(.*?)/^four/', x, ignore.case = TRUE, perl = TRUE, value = TRUE,
     fixed = FALSE, useBytes = FALSE, invert = FALSE)

to extract a porting of text from myfile.txt

zero
one
two
three
four
five

the output I'm expecting is

one
two
three
four

I want to include the "one" and "four" I don't want to ditch them :)

But somehow the regex is not working, The console output is giving no error but no text either... ?

I am using print(b)

Answer 1

I'm not quite clear on what you're looking for, but just for fun...

R> x
[1] "zero"  "one"   "two"   "three" "four"  "five" 

R> grep("one|four", x) # get the position of "one" and "four"
[1] 2 5

Subset x to only include the things between "one" and "four"

R> x[do.call(seq, as.list(grep("one|four", x)))]
[1] "one"   "two"   "three" "four" 

Answer 2

gsub('one(.*)four','\\1',paste(x,collapse=''))
[1] "zerotwothreefive"

or to get space between words :

gsub('one(.*)four','\\1',paste(dat,collapse=' '))
[1] "zero  two three  five"

Edit after Gsee comment:

 gsub('.*(one.*four).*','\\1',paste(dat,collapse=' '))
[1] "one two three four"

But I think here no need to use regular expression :

 dat[seq(which(dat == 'one'),which(dat == 'four'))]
[1] "one"   "two"   "three" "four" 

of course you can use min if the previous index in which are not in the good order.