Collapse columns by grouping variable (in base)

Question

I have a text variable and a grouping variable. I\'d like to collapse the text variable into one string per row (combine) by factor. So as long as the group column says

Answer 1

This makes use of rle to create an id to group the sentences on. It uses tapply along with paste to bring the output together

## Your example data
dat <- structure(list(text = c("Computer is fun. Not too fun.", "No its not, its dumb.", 
"How can we be certain?", "There is no way.", "I distrust you.", 
"What are you talking about?", "Shall we move on?  Good then.", 
"Im hungry.  Lets eat.  You already?"), group = structure(c(2L, 
2L, 1L, 2L, 2L, 1L, 1L, 2L), .Label = c("f", "m"), class = "factor")), .Names = c("text", 
"group"), row.names = c(NA, 8L), class = "data.frame")


# Needed for later
k <- rle(as.numeric(dat$group))
# Create a grouping vector
id <- rep(seq_along(k$len), k$len)
# Combine the text in the desired manner
out <- tapply(dat$text, id, paste, collapse = " ")
# Bring it together into a data frame
answer <- data.frame(text = out, group = levels(dat$group)[k$val])