I have a vector of strings.
d <- c("Mon","Tues","Wednes","Thurs","Fri","Satur","Sun")
for which I want to paste the string "day" on each element of the vector in a way similar to this.
week <- apply(d, "day", paste, sep='')
No need for apply(), just use paste():
R> d <- c("Mon","Tues","Wednes","Thurs","Fri","Satur","Sun")
R> week <- paste(d, "day", sep="")
R> week
[1] "Monday" "Tuesday" "Wednesday" "Thursday"
[4] "Friday" "Saturday" "Sunday"
R>
Other have already indicated that since paste is vectorised, there is no need to use apply in this case.
However, to answer your question: apply is used for an array or data.frame. When you want to apply a function over a list (or a vector) then use lapply or sapply (a variant of lapply that simplifies the results):
sapply(d, paste, "day", sep="")
Mon Tues Wednes Thurs Fri Satur
"Monday" "Tuesday" "Wednesday" "Thursday" "Friday" "Saturday"
Sun
"Sunday"
来源：https://stackoverflow.com/questions/6984796/how-to-paste-a-string-on-each-element-of-a-vector-of-strings-using-apply-in-r