r - How do I replace the string exactly using gsub()

Question

I have a corpus: txt = "a patterned layer within a microelectronic pattern." I would like to replace the term "pattern" exactly by "form", I try to write a code:

txt_replaced = gsub("pattern","form",txt)

However, the responsed corpus in txt_replaced is: "a formed layer within a microelectronic form."

As you can see, the term "patterned" is wrongly replaced by "formed" because parts of characteristics in "patterned" matched to "pattern".

I would like to query that if I can replace the string exactly using gsub()? That is, only the term with exactly match should be replaced.

I thirst for a responsed as below: "a patterned layer within a microelectronic form."

Many thanks!

Answer 1

As @koshke noted, a very similar question has been answered before (by me). ...But that was grep and this is gsub, so I'll answer it again:

"<" is an escape sequence for the beginning of a word, and ">" is the end. In R strings you need to double the backslashes, so:

txt <- "a patterned layer within a microelectronic pattern."
txt_replaced <- gsub("\<pattern\>","form",txt)
txt_replaced
# [1] "a patterned layer within a microelectronic form."

Or, you could use instead of < and >. matches a word boundary so it can be used at both ends>

txt_replaced <- gsub("\bpattern\b","form",txt)

Also note that if you want to replace only ONE occurrence, you should use sub instead of gsub.