Find all sequences with the same column value

Question

I have the following data frame:

╔══════╦═════════╗
║ Code ║ Airline ║
╠══════╬═════════╣
║    1 ║ AF      ║
║    1 ║ KL      ║
║    8 ║ AR      ║
║    8 ║ A         


        

Answer 1

split helps. Here's a fully reproducible EDIT that works w/o any additional package. Works with the OPs data.frame - changed it after OP added a reproducible dataset.

# strip white space in Airline names:
dat$Airline <- gsub(" ","",dat$Airline)
li <- split(dat,factor(dat$Code))
do.call("rbind",lapply(li,function(x) 
data.frame(Airline = x[1,2],
         SharedWith = paste(x$Airline[-1]
                            ,collapse=",")
))
)