r - Count number of connenction in data.frame dplyr -

i have data.frame:

 df <- data.frame(id = rep(1:4, each = 3),x = c("a","b","c","d","e","a","a","c","d","a","c","e")) 

i want count connections inside each id: output want get:

connections    |num. of connections    - b       | 1    b - c       | 1    c - d       | 1    - c       | 3    - e       | 2    - d       | 2    d - e       | 1    c - e       | 1 

how in dplyr?

using dplyr , combn

library(dplyr) df %>%     group_by(id) %>%     mutate(connections=c(combn(as.character(x),2,         fun=function(x) paste(sort(x), collapse=" - ")))) %>%     group_by(connections) %>%     summarise(numconn=n())  #   connections numconn  #1       - b       1  #2       - c       3  #3       - d       2  #4       - e       2  #5       b - c       1  #6       c - d       1  #7       c - e       1  #8       d - e       1 

or same approach data.table

library(data.table) setdt(df)[,combn(as.character(x),2, fun= function(x)            paste(sort(x), collapse=" - ")) , by=id][                     ,list(numconn=.n), by=list(connections=v1)]  #    connections numconn #1:       - b       1 #2:       - c       3 #3:       b - c       1 #4:       d - e       1 #5:       - d       2 #6:       - e       2 #7:       c - d       1 #8:       c - e       1