I search through the questions and able to replace • in my first set of command. But when I apply to my corpus, it doesn't work, the • still appear. The corpus has 6570 elements,2.3mb, so it seems to be valid.
> x <- ". R Tutorial"
> gsub("•","",x)
[1] ". R Tutorial"
> removeSpecialChars <- function(x) gsub("•","",x)
> corpus2=tm_map(corpus2, removeSpecialChars)
> print(corpus2[[6299]][1])
[1] "• R tutorial • success– october"
> ##remove special characters