Convenience functions for https://openexchangerates.org/

exchange-rates.R

# (1) Get a free plan from https://openexchangerates.org/signup/free
# (2) Tell this function your API key:
# from this section of the site: https://openexchangerates.org/account/app-ids
# Sys.setenv(OER_KEY = "paste-your-very-long-numeric-string-here")
Sys.setenv(OER_KEY = "OER_KEY")

library(glue)
library(tidyverse)
get_day <- function(day) {
  u <- glue("https://openexchangerates.org/api/historical/{day}.json?app_id=\\
            {Sys.getenv('OER_KEY')}")
  
  res <- jsonlite::fromJSON(u)
  
  # convert timestamp to date object
  # http://stackoverflow.com/questions/13456241/convert-unix-epoch-to-date-object-in-r
  res$rates$date <- as.POSIXct(
    res$timestamp,
    origin = "1970-01-01"
  )
  data.frame(res$rates)
}

get_rates <- function(start = end - 3, 
                      end = Sys.Date()) {
  
  days <- seq(start, 
              end, 
              by = "1 day")
  
  map_dfr(days, get_day)
}

data <- get_rates()

data %>% 
   select(AUD,
          NZD,
          date)

#>       AUD      NZD                date
#> 1 1.477168 1.566082 2019-08-27 09:59:59
#> 2 1.480451 1.571440 2019-08-28 09:59:59
#> 3 1.483777 1.578108 2019-08-29 09:59:59
#> 4 1.486302 1.584042 2019-08-29 14:00:00