casefold

Usage
casefold(x, upper = FALSE)
大小写转换
Arguments
upper→逻辑值，是否转换为大写，默认为FALSE
Example

casefold用法

tolower&toupper

Usage
tolower(x)→转换为小写
toupper(x)→转换为大写
Example

tolower&toupper用法

推论inference

From above examples,we can know that:
toupper(x) = casefold(x,upper = T)