Consider the following string:
string = "I have #1 file and #11 folders"
I would like to replace the pattern #1 with the word one, but I don't want to modify th #11. The result should be:
string = "I have one file and #11 folders"
I have tried:
string = gsub("#1", "one, string, fixed = TRUE)
but this replaces both #1 and #11. I have also tried:
string = gsub("^#1$", "one, string, fixed = TRUE)
but this doesn't replace anything since the pattern is part of a string that contains spaces.
Please note that if the initial string looked like:
string = "I have #1 file blah blah blah and #11 folders"
I would want the result to be:
string = "I have 1 file blah blah blah and #11 folders"
In other words, I literally just want to change the exact pattern #1 without touching the rest of the string. Is that possible?
If you use the perl=TRUE argument to tools like gsub then the perl regex engine will be used which has some options that could help.
The pattern "#1\\b" will match #1 followed by a word boundary, so it would match #1, but not #11 (since there is no boundary between the 2 1's). There are also tools for positive and negative look ahead which look for things following your pattern (like the word file maybe), but does not include them in the part to be replaced.
I'm not sure if I understood right, but does this help -
a <- "I have #1 file and #11 folders"
b <- "I have #1file and #11 folders"
c <- "I have #1,file and #11 folders"
> gsub(x = a, pattern = "#1.*file", replacement = "one file")
[1] "I have one file and #11 folders"
> gsub(x = b, pattern = "#1.*file", replacement = "one file")
[1] "I have one file and #11 folders"
> gsub(x = c, pattern = "#1.*file", replacement = "one file")
[1] "I have one file and #11 folders"
Use the space after #1 to your advantage:
gsub("#1 ", "one ", string, fixed = TRUE)
[1] "I have one file and #11 folders"
来源：https://stackoverflow.com/questions/20223071/matching-entire-string-in-r