aggregate in R by permutations of column values

Question

Background: I\'m working with origin-destination data. I would like to calculate the proportional flow between each pair of cities. However, I\'m finding it dif

Answer 1

Here is one solution:

library(dplyr)
df$pair <- ifelse(df$Destination < df$Origin,
                  paste(df$Destination, df$Origin, sep = ','),
                  paste(df$Origin, df$Destination, sep = ','))

df %>% group_by(pair) %>% summarise(Flow = paste(Flow, collapse = ' + '))

Source: local data frame [2 x 2]

   pair    Flow
  (chr)   (chr)
1   a,b f1 + f2
2   c,d f3 + f4

The Flow column is obviously paste using character vectors since that is what you gave. You can modify to sum(Flow) if you have numeric values.

EDITED: Sorry, earlier, I was summing wrong column. Fixed.