[R] Month end calculations

[Jeff Ryan]

Shubha et al,

I forgot that the period methods may not work without the full
package.  So either just download the current CRAN version 0.1-0 or
version 0.1-3 from quantmod.com, a new more complete version will be
up with a week or two.

For completeness here is my months method for zoo objects:

> quantmod:::months.zoo
function (x, abbreviate = FALSE)
{
    format(index(x), ifelse(abbreviate, "%m", "%B"))
}
<environment: namespace:quantmod>

The primary difference is that abbreviate=TRUE will return the month
NUMBER, not the standard English abbreviation.  For the other methods
it is probably wiser to install the package as opposed to my obviously
deficient copy and paste method.

Thanks,
Jeff Ryan

On 8/30/07, Jeff Ryan <jeff.a.ryan at gmail.com> wrote:
> Shubha,
>
> I apologize if this is a bit late - consequence of digest summary preference.
>
> If I understand what you need, it is to calculate the value at month
> end given a data object. For zoo objects the following should do what
> you need. Actually is part of my new package on CRAN quantmod -
> basically a workflow management tool for quant finance modelling.
> Also visible at www.quantmod.com
>
> If you convert your data.frame to a zoo object (designed for ordered
> obs. -  e.g. time-series)
>
> # for your data - which I don't know : )
> zoo.ts <- zoo(youdataframe[,-1],as.Date(yourdataframe[,1]))
>
> #                            ^
>           ^
> #                           ^ ^
>         ^ ^
> #                     minus 'date' column                  the 'date'
> column - in CCYY-MM-DD format
>
>
> My example:
>
> A zoo time series object consisting of 231 days:
>
> > zoo.ts <- zoo(rnorm(231),as.Date(13514:13744))
> > start(zoo.ts)
> [1] "2007-01-01"
> > end(zoo.ts)
> [1] "2007-08-19"
>
> # these are the end points of each period
> > breakpoints(zoo.ts,months,TRUE)
> [1]   0  31  59  90 120 151 181 212 231
>
> # get the associated values
> > zoo.ts[breakpoints(zoo.ts,months,TRUE)]
>   2007-01-31   2007-02-28   2007-03-31   2007-04-30   2007-05-31   2007-06-30
> -0.008829668 -2.207802921  0.171705151 -1.820125167  1.776643162  0.884558259
>   2007-07-31   2007-08-19
>  0.655305543  0.191870144
>
> You can also apply a function inside each of these periods (intervals)
> with the function
> period.apply:
>
> e.g. the standard deviation of each period would be had with:
>
> > period.apply(zoo.ts,breakpoints(zoo.ts,months,TRUE),FUN=sd)
> [1] 0.9165168 1.2483743 1.0717529 1.2002236 0.9568443 0.8112068 0.8563814
> [8] 0.8671502
>
> The functions (and many others) are in quantmod - on CRAN and most up
> to date at www.quantmod.com
>
> For those who'd rather just have the functions:
>
> breakpoints <-
> function (x, by = c(weekdays, weeks, months, quarters, years), ...)
> {
>     if (length(by) != 1)
>         stop("choose ONE method for \"by\"")
>     by <- match.fun(by)
>     breaks <- which(diff(as.numeric(by(x, ...))) != 0)
>     breaks <- c(0, breaks, NROW(x))
>     return(breaks)
> }
>
>
> period.apply <-
> function (x, INDEX, FUN, ...)
> {
>     FUN <- match.fun(FUN)
>     y <- NULL
>     for (i in 1:(length(INDEX) - 1)) {
>         sindex <- (INDEX[i] + 1):INDEX[i + 1]
>         dat <- x[sindex]
>         y <- c(y, FUN(dat, ...))
>     }
>     return(y)
> }
>
> Jeff Ryan
>