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

An an igraph approach

library(igraph)

g <- graph_from_data_frame(dat)

# Find neighbours for select nodes
ne <- setNames(ego(g,2, nodes=as.character(dat$Airline), mindist=2), dat$Airline)
ne
#$`AF  `
#+ 1/7 vertex, named:
#[1] KL  

#$`KL  `
#+ 1/7 vertex, named:
#[1] AF  
---
---

# Get final format
data.frame(Airline=names(ne), 
           Shared=sapply(ne, function(x)
                                      paste(V(g)$name[x], collapse=",")))
#   Airline Shared
# 1      AF     KL
# 2      KL     AF
# 3      AR  AZ,DL
# 4      AZ  AR,DL
# 5      DL  AR,AZ