Finding distances between cities?

Question

After messing with my code for a while and fixing error messages, I was able to run the code with no errors, but it did not do what I expected and calculate the distances between each city.

#Separate cities want to find distance between
count = 0
for (i in 1:n_cities) {
    { 
       for (j in i:n_cities-1)
        count = count + 1
    }
        city_1 <- cities3[i,]
        city_2 <- cities3[i+count,]
        rad <- (pi/180)
        distance <- 6371 * acos( (sin(city_1$latitude*rad)*sin(city_2$latitude*rad)) + (cos(city_1$latitude*rad)*cos(city_2$latitude*rad)*cos((city_1$longitude - city_2$latitude)*rad)) )
        City.1 <- city_1$city
        City.2 <- city_2$city
        cities3[[City.1]]
        cities3[[City.2]]
        cities3[[distance]]
}

I need to find the distance between each city in the data frame, so if I am given 4 cities in my data, I need to find 6 distances. I think my problem is with the counter and running the loop throughout my dataset. Does anyone know what I am doing wrong with the counter and cycling through the loop? I think everything past that should work.

I think that you probably wanted i to go from 1 to n_cities - 1 and j to go from i + 1 to n_cities — G5W, Feb 25 '18 at 21:51
I'd recommend this post for more methods on calculating the distance between two coordinates: [Geographic / geospatial distance between 2 lists of lat/lon points (coordinates)](https://stackoverflow.com/questions/31668163/geographic-geospatial-distance-between-2-lists-of-lat-lon-points-coordinates) — Cristian E. Nuno, Feb 25 '18 at 23:09
G5W, I tried that before and got error message: Error in .subset2(x, i, exact = exact) : attempt to select less than one element in get1index — ping88, Feb 26 '18 at 02:56

score 1 · Answer 1 · answered Feb 26 '18 at 22:58

Not the prettiest but something like this:

# load the city data
lines<-"Minsk, 53.85, 27.5,
Brussels, 50.833333, 4.333333,
Addis Ababa, 9.05, 38.7,
Helsinki, 60.133333, 25, 
Berlin ,52.533333, 13.416667, 
Hong Kong, 22.25, 114.166667"
con <- textConnection(lines)
data <- read.csv(con, header=T)
colnames(data)<-c("city", "lat", "lon")

# Get all combinations from city to city
data2<-expand.grid(data$city, data$city)
colnames(data2)<-c("city", "city2")
data2<-merge(data, data2, by.x="city")
data2<-merge(data, data2, by.x="city", by.y="city2")
data2<-unique(data2[c(1,2,3,5,6,7)])

# Calculate the distances
library(geosphere)
library(dplyr)
data3<-data2 %>% rowwise() %>% 
  mutate(distance = distHaversine(c(lon.x, lat.x), c(lon.y, lat.y)))
data3<-data3[!duplicated(data3$distance) & data3$distance!=0, ]

Finding distances between cities?

1 Answers1