R regex - removing pattern from ends

Question

Suppose I have a string that looks like so:

x <- "NNNNAAAJNFHANFFADN"

How would I only remove the N's from the ends to get:

"AAAJNFHANFFAD"

Answer 1

Just match and remove the N 's which exists at the start or at the end through gsub .

gsub("^N+|N+$", "", x)

• ^N+ matches one or more N 's which exists at the start.
• | Alternation operator.
• N+$ Matches one or more N's which exists at the end.

Example:

> x <- "NNNNAAAJNFHANFFADN"
> gsub("^N+|N+$", "", x)
[1] "AAAJNFHANFFAD"

Answer 2

gsub("^N*([A-Z]*?)N*$", "\\1", x)

You can use \\1 to backreference here.See demo.

https://regex101.com/r/uF4oY4/66

Answer 3

Use as

gsub("(^N{1,}|N{1,}$)","",x)

https://regex101.com/r/uF4oY4/69