Using the subsetting operator :: in quantmod with variables - r

Question

How do I apply a user initialized date variables as the start and end values of the subset operator :: from the R-package, quantmod?
For example, when I apply user initialized date variables,
end.date <- Sys.Date()
start.date <- end.date - 5*365 #5- years to-date
start.date.char <- as.character(start.date)
end.date.char <- as.character(end.date)
to get 5-years of stock data
library(quantmod)
getSymbols("GILD",src="yahoo")
GILD.5YTD <- GILD['start.date.char::end.date.char']
I get the following error:
Error in if (length(c(year, month, day, hour, min, sec))
== 6 && c(year, :
missing value where TRUE/FALSE needed
In addition: Warning messages:
1: In as_numeric(YYYY) : NAs introduced by coercion
2: In as_numeric(MM) : NAs introduced by coercion
3: In as_numeric(DD) : NAs introduced by coercion
4: In as_numeric(YYYY) : NAs introduced by coercion
5: In as_numeric(MM) : NAs introduced by coercion
6: In as_numeric(DD) : NAs introduced by coercion
I'm sure this is a basic question, but I'm a newbie.

Answer 1

There are convenient high-level functions to subset an xts object as returned, e.g., by quantmod's getSymbols().
For a time-based subset, the last() function from the xts package (automatically loaded by quantmod) is quite handy:
library(quantmod)
getSymbols("GILD",src="yahoo")
GILD_last5Years <- last(GILD, "5 years")
#> head(GILD_last5Years)
# GILD.Open GILD.High GILD.Low GILD.Close GILD.Volume GILD.Adjusted
#2012-01-03 41.46 41.99 41.35 41.86 19564000 20.46895
#2012-01-04 41.95 42.06 41.70 42.02 16236000 20.54719
#2012-01-05 42.04 42.97 42.00 42.52 18431800 20.79168
#2012-01-06 42.38 43.10 42.20 42.78 15542000 20.91882
#2012-01-09 42.49 42.99 42.35 42.73 16801200 20.89437
#2012-01-10 43.10 45.04 42.94 44.25 30110000 21.63763
This can be combined with an equivalent function first() to select a specific time span within the series.

Answer 2

Your current argument to [.xts is just the character value 'start.date.char::end.date.char' and would not be evaluated further, since R is not a macro language. Try instead to build the desired character value, which I believe is: "2011-08-28::2016-08-26". So this succeeds:
GILD.5YTD<-GILD[paste(start.date.char, end.date.char, sep="::")]
str(GILD.5YTD)
#-------
An ‘xts’ object on 2011-08-29/2016-08-25 containing:
Data: num [1:1257, 1:6] 39 39.7 40.2 39.8 39 ...
- attr(*, "dimnames")=List of 2
..$ : NULL
..$ : chr [1:6] "GILD.Open" "GILD.High" "GILD.Low" "GILD.Close" ...
Indexed by objects of class: [Date] TZ: UTC
xts Attributes:
List of 2
$ src : chr "yahoo"
$ updated: POSIXct[1:1], format: "2016-08-26 17:00:52"
So technically the :: is not acting as an R operator, but is being parsed by the [.xts function. Pkg:quantmod is built on top of the xts;package. The "::" function is really for package-directed function access for exported functions of installed packages.

Answer 3

The reason for your errors are that you are submitting the variables within a string which can not work. ( By the way you do not have to convert the date into as.character as in your example as pasting will do that for you). Using paste0 like so will subset your data accordingly:
GILD.5YTD<-GILD[paste0(start.date.char,'::',end.date.char)]