API Call per Row of data frame in R

I have one column in a dataframe that consists of ticker codes such as AAPL (for Apple stock), TWTR (for Twitter), and many more. I am trying to create a new column where it will return the number of stocks for each ticker code that have been computed from the stock API data.

But when I ran the code below, the new column "Stock Quantity" returned NA for every row. Does anyone have the solution to this?

library(Quandl)

portfolio <- data.frame(Code=c("AAPL", "TWTR", "MSFT"),
                startingPeriod=c("2015-01-01", "2015-01-01", "2015-01-01"),
                Investment=c("5000", "10000", "15000"), 
                stringsAsFactors=FALSE)


numberofStock <- function(pf) {

API <- Quandl(paste0("WIKI/", pf$Code), type = "raw", 
            start_date = pf$startingPeriod, end_date=Sys.Date())

pf["StockQuantity"] <- floor(pf$Investment_01 / tail(API$Open,1))

return(pf)
}


numberofStock(portfolio)

Solution

Here's a start.

library(dplyr)

company.initial = 
  portfolio %>%
  mutate(Investment = as.numeric(Investment) ) %>%
  group_by(Code) %>%
  summarize(start_date = min(startingPeriod),
            total_investment = sum(Investment) )

company__date = 
  company.initial %>%
  group_by(Code) %>%
  do(with(.,
     Quandl(paste0("WIKI/", Code), 
            type = "raw",
            start_date = start_date, 
            end_date = Sys.Date() ) ) )

company = 
  company__date %>%
  group_by(Code) %>%
  summarize(last_open = last(Open)) %>%
  left_join(company.initial) %>%
  mutate(StockQuantity = total_investment / last_open)