How do I do an exact string match using gsub in R? [duplicate]

问题

This question already has answers here:

How to grep a word exactly (3 answers)

Closed 5 years ago.

raw = c("MOUNTAIN VIEW","MOUNTAIN")
x = gsub("MOUNTAIN", "MOUNTAIN VIEW", raw, ignore.case = TRUE)

Current output: "MOUNTAIN VIEW VIEW" "MOUNTAIN VIEW"  
Desired output:  "MOUNTAIN VIEW" "MOUNTAIN VIEW"  

I only want to replace the 2nd entry in the raw data MOUNTAIN with MOUNTAIN VIEW. The first entry in raw data is already correct. But when I do gsub it replaces both the occurrences of MOUNTAIN with MOUNTAIN VIEW. Can anyone help me find a way to get around that?

I tried \\b but it didn't work and I understand why. Is there any thing else I can do?

回答1:

Use anchors instead here to match the entire string:

sub('^MOUNTAIN$', 'MOUNTAIN VIEW', raw, ignore.case = TRUE)
# [1] "MOUNTAIN VIEW" "MOUNTAIN VIEW"

If you desire, you can also use a capturing group and backreference it inside the replacement call:

sub('^(MOUNTAIN)$', '\\1 VIEW', raw, ignore.case = TRUE)

回答2:

using agrep -returns vector indices, so you can easily assign a value by using subscripts:

raw[agrep("MOUNTAIN", raw)] <- "MOUNTAIN VIEW" 
raw
[1] "MOUNTAIN VIEW" "MOUNTAIN VIEW"

来源：https://stackoverflow.com/questions/30387685/how-do-i-do-an-exact-string-match-using-gsub-in-r