R - finding pattern in a column and replacing it (more efficient solution)

Question

I have a large data set of passengers per route similar to the following:

routes <- c("MEX-GDL", "ACA-MEX", "CUN-MTY", "MTY-CUN", "GDL-MEX", "MEX-ACA")
pax <- sample(100:500, size = 6, replace = T)
traffic <- data.frame(routes = routes, pax = pax)

   routes pax
   1 MEX-GDL 282
   2 ACA-MEX 428
   3 CUN-MTY 350
   4 MTY-CUN 412
   5 GDL-MEX 474
   6 MEX-ACA 263

I want to group flights if the origin and destination match as to get the total number of passengers in the route - so for example renaming the route MEX-GDL as GDL-MEX or viceversa so I can then use group_by() on the data set.

Kind of like this:

traffic %>% group_by(routes) %>% summarise(sum(pax)) 

I have done the following and it works, but I believe there can be a more efficient way to solve the problem (as it takes quite some time to run):

library(tidyverse)

traffic$routes <- as.character(traffic$routes)

for(route in traffic$routes){
  a <- substring(route, first = 1, last = 3) 
  b <- substring(route, first = 5, last = 7)
  aux <- which(sapply(traffic$routes, str_detect, pattern = paste0(b,"-",a)))
  traffic$routes[aux] <- paste0(a,"-",b)
}

Any suggestions?

Thanks for the help!

Note: it's my first question here, so I hope I complied with all the guidelines.

Answer 1

We can separate into two columns, grouped by the pmax or pmin, get the sum

library(tidyverse)
traffic %>% 
   separate(routes, into = c("Col1", "Col2")) %>%
   group_by(ColN = pmin(Col1, Col2), ColN2 = pmax(Col1, Col2)) %>% 
   summarise(Sum = sum(pax))

Answer 2

data.table version

data: (?I READ THIS)

traffic <- data.frame(routes = I(routes), pax = pax)

library(data.table)
setDT(traffic)[,routes := sapply(strsplit(routes, split="-"), function(x) paste0(sort(x),collapse = "-"))][,.(Sum = sum(pax)), by = routes]

result: (values differ because of sample function)

#    routes Sum
#1: GDL-MEX 621
#2: ACA-MEX 595
#3: CUN-MTY 266

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• If you use data with ?sample use ?set.seed along with it.