gsub error turning upper to lower case in R

Question

I would like to recode some identifiers, from upper case to lower case.

I am not sure what the issue is here.

n = c('AFD.434', 'BSD.23', 'F234.FF')
gsub(pattern = '[[:upper:]]', replacement = '[[:lower:]]', n)

[1] "[[:lower:]][[:lower:]][[:lower:]].434" "[[:lower:]][[:lower:]][[:lower:]].23"  "[[:lower:]]234.[[:lower:]][[:lower:]]"

Any advice?

Answer 1

Your gsub call replaces each occurrence with the literal string "[[:lower:]]".

The simplest solution is to not use regular expressions; simply use tolower() (as already mentioned in the comments / other answers).

One possible approach with regular expressions is the usage of Perl extended mode and the \L modifier to convert to lowercase:

gsub(pattern = '([[:upper:]])', perl = TRUE, replacement = '\\L\\1', n)

This approach

• uses a capturing group (...) to "remember" the match
• uses a backreference \1 to refer to the match in the replacement string
• uses the \L modifier to convert the match to lowercase

See the online help for gsub for further details.