使用R将具有全部CAPS的单词除外，将句子中所有字母从大写转换为小写

Question

I want to convert my data frame of text into lowercase but I do not want to convert the words with all CAPS letters. For example if have a string like

"My friEnd ENRIQUE is nOt GOoD in stuDies"

The output of this should be like

"my friend ENRIQUE is not good in studies"

It converted everything to lowercase except words with all capital letters. I need ar function to do this task.

Answer 1

You can do this with gsub and a (perl compatible) regular expression.

gsub("(\\b\\w*[a-z]\\w*\\b)", "\\L\\1", String, perl=TRUE)
"my friend ENRIQUE is not good in studies"

Putting \\\\b word boundaries insures that this operates on separate words. [az] picks the words that contain at least one lower case letter. The \\\\w* before and after [az] matches any number (including zero) of "word characters" ie letters or numbers. The \\\\L in the substitution pattern converts to lower case.

Answer 2

We can split the string into different words and then find out those words which contain any lower case letter [az] and convert that word to lower case.

word_vec <- strsplit(x, " ")[[1]]
ifelse(grepl('[a-z]', word_vec), tolower(word_vec), word_vec)

#[1] "my"  "friend"  "ENRIQUE" "is"  "not"  "good"  "in"  "studies"

To make it as a single string we can use paste0 with an empty collapse argument.

paste0(ifelse(grepl('[a-z]', word_vec), tolower(word_vec), word_vec), collapse = " ")

#[1] "my friend ENRIQUE is not good in studies"