groups<-c('MyGroup', 'MyGroup', 'MyGroup', 'YourGroup', 'YourGroup', 'YourGroup')
words<-c('hello', 'goodbye', 'bonjour', 'red', 'blue', 'green')

data <- data.frame(groups, words)

group_word <- function(df,group){
 grouped <- df[which(df$groups==group),]
 word<- unique(grouped$words)
 return(word)
}


group_word(data,"YourGroup")
group_word(data,"MyGroup")

> group_word(data,"YourGroup")
[1] red   blue  green
Levels: blue bonjour goodbye green hello red
> group_word(data,"MyGroup")
[1] hello   goodbye bonjour
Levels: blue bonjour goodbye green hello red