mutate function is not updating
Solution 1:
mutate doesn't change the tbl_df in place, it just returns the new, changed tbl_df. You need to save the results:
fltr <- mutate(fltr, cat = "xxxxx")
Solution 2:
As @DavidRobinson pointed out, you are not assigning it back to the same object. To avoid reassigning we could use magrittr's compound assignment pipe-operator - %<>% :
require(dplyr)
require(magrittr)
fltr %<>% mutate(cat="xxxxx")