Select a category in dataframe for operation in r?

Having this dataframe:

dat=data.frame(a=c("ll","pp","ml","ml","v"),value=c(1,2,12,1,2))

I want to multiply by 10 only values correspond to a=ml

>Solution :

Another solution is to use a ifelse statement

dat %>% 
  mutate(value = ifelse(a == "ml", value*10, value))

   a value
1 ll     1
2 pp     2
3 ml   120
4 ml    10
5  v     2