More complicated plumber API example showing how to parse JSON inputs

plumber.R

library(plumber)
library(dplyr)
library(tidyquant)
library(jsonlite)

get_volatility <- function(ticker = 'GOOG') {
  price <- tq_get(ticker, from = "2018-01-01")
  volatility <- price %>% 
    select(date, adjusted) %>% 
    mutate(returns = (log(adjusted) - log(lag(adjusted)))) %>%
    na.omit() %>% 
    summarize(volatility = var(returns)) %>% 
    pull(volatility)
  return(volatility)
}

get_volatilities <- function(json_input) {
  tickers <- fromJSON(json_input)
  volatilities <- sapply(tickers, get_volatility)
  volatilities
}

# create test inputs using toJSON
#tickers <- c('GOOG', 'TSLA')
#test_input <- toJSON(tickers)
#get_volatilities(test_input)


#* @apiTitle Stock Volatilities

#* Return the stock volatilties for the input stock tickers
#* @put /volatilities
function(req) {
  print(req$postBody)
  get_volatilities(req$postBody)
}

#* @apiTitle Stock Volatility

#* Return the stock volatiltiy for the input stock ticker
#* @param ticker The stock ticker
#* @get /volatiltiy
function(ticker = 'GOOG') {
  get_volatility(ticker)
}

## Sample Requests:

#  curl -X PUT "http://ec2-54-202-230-54.us-west-2.compute.amazonaws.com/content/2/volatilities" -H  "accept: application/json"  --data '["GOOG","TSLA"]'
#  curl -X GET "http://ec2-54-202-230-54.us-west-2.compute.amazonaws.com/content/2/volatiltiy?ticker=TSLA" -H  "accept: application/json"