function  person
1                hr       1
2                sls      5
3                mktg     3
4                qlt      7
5                rev      5

Person     function
1             1         hr
2             8         sls & mktg
3             7         qlt
4             5         rev

library(dplyr)

dat <- data.frame(func = c("hr", "sls", "mktg", "qlt", "rev"),
                  person = c(1, 5, 3, 7, 5))

dat %>%
  mutate(func = func %>% as.factor() %>% as.character(),
         func = ifelse(func %in% c("sls", "mktg"), "sls & mktg", func)) %>%
  group_by(func) %>%
  summarize(Person = sum(person))

# A tibble: 4 x 2
  func       Person
  <chr>       <dbl>
1 hr              1
2 qlt             7
3 rev             5
4 sls & mktg      8

merg <- c("sls", "mktg")
dat$func[dat$func %in% merg] <- paste(merg, collapse = " & ")
aggregate(person ~ func, dat, sum)
        func person
1         hr      1
2        qlt      7
3        rev      5
4 sls & mktg      8

dat <- data.frame(
  func = c("hr", "sls", "mktg", "qlt", "rev"),
  person = c(1, 5, 3, 7, 5),
  stringsAsFactors = FALSE
)