How to add quotes around each word in a string in R?

Use gsub

words<-"Monday, Tuesday, Wednesday, Thursday,Friday"
cat(gsub("(\\w+)", '"\\1"', words))
# "Monday", "Tuesday", "Wednesday", "Thursday","Friday"

KISS....

cat(gsub("\\b", '"', words, perl=T))
#"Monday", "Tuesday", "Wednesday", "Thursday","Friday"

\\b called word boundary which matches between a word character (A-Z,a-z,_,0-9) and a non-word character (not of A-Za-z0-9_) or vice-versa..

We can split the words by , to get a list output. We loop through sapply , dQuote the elements and then paste it together with toString which is a wrapper for paste(..., collapse=', ').

sapply(strsplit(words, '[, ]+'), function(x) toString(dQuote(x)))
#[1] "“Monday”, “Tuesday”, “Wednesday”, “Thursday”, “Friday”"

If we need to change the fancy quotes, add FALSE in dQuote

sapply(strsplit(words, '[, ]+'), function(x) toString(dQuote(x, FALSE)))