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

You can do this quickly with tidyr's nest (although unless you first translate Airline as factor to character it's less quick) and merge

 library(tidyr)
 dat$Airline <- as.character(dat$Airline)
 new_dat <- merge(dat, dat %>% nest(-Code, .key= SharedWith), by="Code")

and

> new_dat
  Code Airline SharedWith
1    1      AF     AF, KL
2    1      KL     AF, KL
3    8      AR AR, AZ, DL
4    8      AZ AR, AZ, DL
5    8      DL AR, AZ, DL

an advantage of this solution over some of the others: SharedWith becomes a list-column of data.frame rather than say a character

> str(new_dat$SharedWith)
List of 5
 $ :'data.frame':   2 obs. of  1 variable:
  ..$ Airline: chr [1:2] "AF" "KL"
 $ :'data.frame':   2 obs. of  1 variable:
  ..$ Airline: chr [1:2] "AF" "KL"
 $ :'data.frame':   3 obs. of  1 variable:
  ..$ Airline: chr [1:3] "AR" "AZ" "DL"
 $ :'data.frame':   3 obs. of  1 variable:
  ..$ Airline: chr [1:3] "AR" "AZ" "DL"
 $ :'data.frame':   3 obs. of  1 variable:
  ..$ Airline: chr [1:3] "AR" "AZ" "DL"

so you can then easily (albiet not prettily) index out vectors of the shared values, like:

> new_dat$SharedWith[[1]]$Airline
[1] "AF" "KL"

rather than having to use strsplit or similar