function within a forloop in R

Question

I have a simple function and I would like to run it in a forloop. Many thanks in advance.

library(maps); library(ggplot2)
library(grid); library(sf)
library(dplyr); library(rnaturalearth)


europeanUnion <- c("Austria","Belgium","Bulgaria","Croatia","Cyprus",
                   "Czech Rep.","Denmark","Estonia","Finland","France",
                   "Germany","Greece","Hungary","Ireland","Italy","Latvia",
                   "Lithuania","Luxembourg","Malta","Netherlands","Poland",
                   "Portugal","Romania","Slovakia","Slovenia","Spain",
                   "Sweden")

asian.countries <- c("Japan", "China","India", "Thailand", 
                     "South Korea", "North Korea", "Indonesia",
                     "Philippines", "Singapore", "Vietnam")


#FOR LOOP 
my.continents <- c("europeanUnion", "asian.countries")


my.functn <- function(continent.name) {
  
  world_map <- ne_countries(scale = 50, returnclass = 'sf')
  my.map <- world_map %>% filter(name %in% continent.name)
  
    ggplot() + 
    geom_sf(data = my.map, fill = 'white') + 
    geom_sf(fill = 'white', alpha = .2) + 
    theme(
      panel.background = element_rect(fill = "#666666"),
      panel.grid.major = element_blank(), panel.grid.minor = element_blank() 
    )
}

my.functn(europeanUnion)



for(i in my.continents) {
    print(i)
    my.functn(i)
}

SamR · Accepted Answer · 2022-10-10 08:32:34Z

The main problem is how you define your continents:

my.continents <- c("europeanUnion", "asian.countries")

This means that you loop through a character vector of continent names, rather than the continents that you had defined. You should instead create a list of the vectors you created and loop through that:

my.continents  <- list(europeanUnion, asian.countries)

If you just want to print the plots to the console, you can do:

for(continent in my.continents) {
    print(continent)
    print(my.functn(continent))
}

If you want to save the plot to file then you can do:

for(i in seq_along(my.continents)) {
    p  <- my.functn(my.continents[[i]])
    continent_name  <- names(my.continents[i])
    outfile  <- paste0(continent_name, ".png")
    message("Saving to ", outfile)
    ggsave(outfile, p, width = 12, height = 7.5)
}

NB: In general in loops it is conventional to use i as an index number and a name (e.g. continent) if looping through objects.

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