R is passing list index value as numeric, how to force pass as characters

Question

I have some code which passes a list containing some strings to another function. Thing is the new function doesn't use the string associated with the index, but rather uses the index number.

How do I force it to use the string value behind the index value?

My code

  for (i in 1:length(cList)) {

    cList[i] <- GetData(cList[i], StartMonth, StartNumberofMonth, StartYear, EndMonth, EndNumberofMonth, EndYear)

      }


GetData <- function (TickerID, StartMonth, StartNumberofMonth, StartYear, EndMonth, EndNumberofMonth, EndYear) {

  url1 <- "http://real-chart.finance.yahoo.com/table.csv?s="
  url2 <- paste0(TickerID, "&a=", StartMonth-1, "&b=")
  url3 <- paste0(StartNumberofMonth, "&c=", StartYear)
  url4 <- paste0("&d=", EndMonth -1, "&e=", EndNumberofMonth)
  url5 <- paste0("&f=", EndYear, "&g=d&ignore=.csv")
  #/ Generate CSV URL link
      url.final <- paste(url1, url2, url3, url4, url5)

}

When I write print (url.final) I get

[1] "http://real-chart.finance.yahoo.com/table.csv?s= 4&a=1&b= 1&c=2013 &d=1&e=1 &f=2015&g=d&ignore=.csv"

TickerID List

[1] BABA
Levels: ABBV ABEV ACT BABA KMI LFC MA ORCL TSM UPS

As you can see, the index value has been used, not the string behind it. I already tried casting TickerID with as.character, with the same result (not working).

Answer 1

The error is cList is a list, so you cannot cast directly to character the component you get with cList[i], because this is also a list!

If you have myList = list(a=1, b=2, c=3), myList[1] and myList[1:2] are lists (try class(myList[1]) and class(myList[1:2]) to check). On the other hand, myList[[1]] provides you with the content of the first element of the list, which is numeric (try class(myList[[1]])).

To keep your approach, you can unlist your list (with just one element) using this:

cList[i] <- GetData(as.character(unlist(cList[i])), StartMonth, StartNumberofMonth, StartYear, EndMonth, EndNumberofMonth, EndYear)

or index directly the contents of the i-th element of the list using the doble brace:

cList[i] <- GetData(as.character(cList[[i]]), StartMonth, StartNumberofMonth, StartYear, EndMonth, EndNumberofMonth, EndYear)