R, script/function for retrieving more stocks - r

Question

I'm a newbye in R and I've seen several posts about downloading more stocks, but for a reason or another they don't work as suggested.
My purpose is to download a vector of stocks and create a whole xts-matrix containing only Close prices for every stock (so a nobservations x 3 columns).
Anyway, I'd like to start from a basic script that doesn't work properly:
library(quantmod)
ticker=c("KO","AAPL","^GSPC")
for (i in 1:length(ticker)) {
simbol=as.xts(na.omit(getSymbols(ticker[i],from="2016-01-01",auto.assign=F)))
new=Cl(simbol)
merge(new[i])
}
It would be even better to write a function(symbols) that allows me to call whenever I need to just change the name of the stocks to download.
Thanks to everyone

Answer 1

This is how I would do what you want with a function wrapper (which is a pretty common kind of manipulation with xts):
ticker=c("KO","AAPL","^GSPC")
collect_close_series <- function(ticker) {
# Preallocate a list to store the result from each loop iteration (Note: lapply is another alternative to a direct loop)
lst <- vector("list", length(ticker))
for (i in 1:length(ticker)) {
symbol <- na.omit(getSymbols(ticker[i],from="2016-01-01",auto.assign = FALSE))
lst[[i]] <- Cl(symbol)
}
# You have a list of close prices. You can combine the objects in the list compactly using do.call; this is a common "data manipulation pattern" with xts objects.
rr <- do.call(what = merge, lst)
rr
}
out <- collect_close_series(ticker)
More advanced (better code design): You could write cleaner code by writing a function that handles each symbol (rather than a function that wraps and passes in all the symbols together) and then run lapply on it:
per_sym_close <- function(tick) {
symbol <- na.omit(getSymbols(tick,from="2016-01-01",auto.assign = FALSE))
Cl(symbol)
}
out2 <- do.call(merge, lapply(X = ticker, FUN = per_sym_close))
This gives the same result.
Hope this helps getting you started toward writing good R code!