R/Return.calculate.R

In PerformanceAnalytics: Econometric Tools for Performance and Risk Analysis

#' calculate simple or compound returns from prices
#' 
#' calculate simple or compound returns from prices
#' 
#' Two requirements should be made clear.  First, the function
#' \code{Return.calculate} assumes regular price data.  In this case, we
#' downloaded monthly close prices.  Prices can be for any time scale, such as
#' daily, weekly, monthly or annual, as long as the data consists of regular
#' observations.  Irregular observations require time period scaling to be
#' comparable.  Fortunately, \code{\link[xts]{to.period}} in the \code{xts}
#' package, or the \code{\link[zoo]{aggregate.zoo}} in the \code{zoo} package
#' supports supports management and conversion of irregular time series.
#' 
#' Second, if corporate actions, dividends, or other adjustments such as time-
#' or money-weighting are to be taken into account, those calculations must be
#' made separately. This is a simple function that assumes fully adjusted close
#' prices as input.  For the IBM timeseries in the example below, dividends and
#' corporate actions are not contained in the "close" price series, so we end
#' up with "price returns" instead of "total returns".  This can lead to
#' significant underestimation of the return series over longer time periods.
#' To use adjusted returns, specify \code{quote="AdjClose"} in
#' \code{\link[tseries]{get.hist.quote}}, which is found in package
#' \code{tseries}.
#' 
#' We have changes the default arguments and settings for \code{method}
#' from \code{compound} and \code{simple} to \code{discrete} and 
#' \code{log} and \code{discrete} to avoid confusing between the return type
#' and the chaining method.  In most of the rest of \code{PerformanceAnalytics},
#' compound and simple are used to refer to the \emph{return chaining} method used for the returns.
#' The default for this function is to use discrete returns, because most other package 
#' functions use compound chaining by default.
#'  
#' @aliases CalculateReturns Return.calculate
#' @param prices data object containing ordered price observations
#' @param method calculate "discrete" or "log" returns, default discrete(simple)
#' @author Peter Carl
#' @seealso \code{\link{Return.cumulative}}
#' @references Bacon, C. \emph{Practical Portfolio Performance Measurement and
#' Attribution}. Wiley. 2004. Chapter 2 \cr
###keywords ts multivariate distribution models
#' @examples
#' 
#'   \dontrun{
#'     require(quantmod)
#'     prices = getSymbols("IBM", from = "1999-01-01", to = "2007-01-01")
#'   }
#'   \dontshow{
#'     data(prices)
#'   }
#' R.IBM = Return.calculate(xts(prices), method="discrete")
#' colnames(R.IBM)="IBM"
#' chart.CumReturns(R.IBM,legend.loc="topleft", main="Cumulative Daily Returns for IBM")
#' round(R.IBM,2)
#' @export
Return.calculate <-
function(prices, method = c("discrete","log","difference"))
{ # @ author Peter Carl

    #  Calculate returns from a price stream

    # Required inputs

    # Prices: data object containing ordered price observations
    # method: "simple", "compound"

    # FUNCTION:

    method = method[1]
    pr = checkData(prices, method = "xts")

    if(method=="simple" || method=='discrete' || method=="arithmetic"){
        #Returns = pr/pr[-nrow(pr), ] - 1
        Returns = pr/lag.xts(pr) - 1
        xtsAttributes(Returns) <- list(ret_type="discrete")
        #EB: I think this should be more abstract, to cover "level" (e.g. Price), "difference", "residuals", etc.
        xtsAttributes(Returns) <- list(coredata_content = "discreteReturn")
        
    }
    if(method=="compound" || method=='log' || method == "continuous") {
        Returns = diff(log(pr))
        xtsAttributes(Returns) <- list(ret_type="log")
        xtsAttributes(Returns) <- list(coredata_content = "logReturn")
    }
    if(method=="diff" || method=='difference') {
      Returns = diff(pr)
      # xtsAttributes(Returns) <- list(ret_type="diff")
      xtsAttributes(Returns) <- list(coredata_content = "difference")
    }
    
    #maybe set to pr in the body instead of Returns
    xtsAttributes(pr)$coredata_content <- xtsAttributes(Returns)$coredata_content
    reclass(Returns,match.to=pr)
}

#' @rdname Return.calculate
#' @export
CalculateReturns <- 
function(prices, method = c("discrete","log"))
{ # @ author Peter Carl
    Return.calculate(prices=prices, method=method)
}
###############################################################################
# R (http://r-project.org/) Econometrics for Performance and Risk Analysis
#
# Copyright (c) 2004-2020 Peter Carl and Brian G. Peterson
#
# This R package is distributed under the terms of the GNU Public License (GPL)
# for full details see the file COPYING
#
# $Id$
#
###############################################################################