[R-SIG-Finance] Fwd: [R] dynamic runSum

[Brian G. Peterson]

It doesn't sound like you want the 'running' sum.  It sounds like you 
want the sum with a different lookback.

set.seed(987654)
require(foreach)
x<-xts(cumsum(1+rnorm(100,.5,.1)),order.by=as.Date(1:100))
colnames(x)<-'Prices'
x$Lookback<-round(abs(rnorm(100,5,3)))
x$Lookback[1:15] <- 1:15
x$variable_sum <- foreach(i=1:nrow(x), .combine=c) %do%
                   {z <- sum(x$Prices[(i-x$Lookback[i]):i])}

Regards,

Brian

On 08/08/2014 07:08 AM, Ilya Kipnis wrote:
> I am echoing this question. The only thing I can think of is to do
> however many separate runSums, and then just loop across columns. It's
> relevant to me due to John Ehlers's algorithms having a dynamic
> lookback period. Thanks.
>
> On Fri, Aug 8, 2014 at 2:49 AM, amarjit chandhial
> <a.chandhial at btinternet.com> wrote:
>>
>> Hello,
>>
>>
>> I am cross-posting to R-finance as this is finance-orientated.
>>
>>
>>
>> Amarjit
>>
>>
>>
>> ----Original message----
>> >From : a.chandhial at btinternet.com
>> Date : 07/08/2014 - 14:32 (GMTST)
>> To : r-help at r-project.org
>> Subject : [R] dynamic runSum
>>
>> Hello,
>> runSum calculates a running sum looking back a fixed distance n, e.g. 20.
>> How do I calculate a dynamic runSum function for an xts object?
>> In
>> otherwords, I want to calculate a running sum at each point in time
>> looking back a variable distance. In this example, values governed by
>> the vector VL.
>> Here's a minimum reproducible example:
>>
>>   library(quantstrat)
>> symbols = c('^GSPC')
>>
>>   start.date <- as.Date("2010-01-01")
>>   end.date <- as.Date("2013-12-31")
>>
>   getSymbols(symbols, from=as.character(start.date), to=as.character(end.date),adjust=T)
>>
>>   "acF1" <- function(x, n1=5, n2=10, n3=20, nacF1=25, n0=20, ...) {
>>      var1 <- x - lag(x,1,na.pad=T)
>>      var2 <- runSD(x, n=n1, sample=TRUE, cumulative=FALSE)
>>      var3 <- runMean(var2, n=n2, cumulative=FALSE)
>>      VL <- ifelse( trunc(n3/(var2/var3))>nacF1, nacF1, trunc(n3/(var2/var3)))
>>      p_pos <- ifelse(var1>=0, var1, 0)
>>      out1 <- runSum(p_pos,  n=n0, cumulative=FALSE)
>>
>>      res <- cbind(var1, var2, var3, VL, p_pos, out1)
>>      colnames(res) <- c("var1","var2","var3","VL", "p_pos", "out1")
>>
>>      reclass(res)
>>   }
>>
>>
>>   acf1 <- acF1( GSPC[,c("GSPC.Close")], n1=5, n2=10, n3=20, nacF1=25, n0=20)
>>   acf1
>>
>>
>> So on
>> 2010-02-02, I want runSum to be looking back 23 points as governed by VL , not 20 points
>> 2010-02-03, I want runSum to be looking back 24 points as governed by VL,  not 20 points
>>   etc etc
>>   2013-12-31, I want runSum to be looking back 25 points as governed by VL, not 20 points
>>
>>
>> Amarjit
>>
>>
>>   ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
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>
> _______________________________________________
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>

-- 
Brian G. Peterson
http://braverock.com/brian/
Ph: 773-459-4973
IM: bgpbraverock