[18934] in s-news-athena
[S] summary(2): rewrite a loop
daemon@ATHENA.MIT.EDU (fan@katan.cybercom.net)
Fri Aug 13 11:08:08 1999
From: fan@katan.cybercom.net
Date: Fri, 13 Aug 1999 10:59:06 -0400
Message-Id: <199908131459.KAA25447@katan.cybercom.net>
To: s-news@wubios.wustl.edu
Peter Wolf points that the cumsum() can be used to solve the (equi-weighted)
moving average question. It is by far the best solution, better than matrix
solution and filter() function. Refer to the first summary I posted.
E.G.
x<-1:1000
n <- 30
result3 <- cumsum(x)
result3 <- diff(c(0, result3), lag = n)/n
[original question]
----------------
> From: fan@katan.cybercom.net
> Date: Tue, 10 Aug 1999 15:54:04 -0400
> To: s-news@wubios.wustl.edu
> Subject: [S] rewrite a loop
> X-loop: s-news
>
>
> In computing a moving average of a sequence, I look for a way not to use
> the loop? Example:
>
> #x is a sequence of 1000 data points
> x<-1:1000
> #y is the 30-term moving average of x;
> #i.e.: y[i] <- mean(x[i:(i+29)]), i = 1, ..., 971
> #or in vector form: y <- (x[1:971]+x[2:972]+...+x[30:1000])/30
> #Surely, a loop solves it:
> y <- rep(0,length(x)-30+1)
> for (j in 1:30)
> y <- y + x[i:(i+970)]
> y <- y/30
>
> I feel some better codes can work on this job efficiently without using loop.
> If you have an idea, let me know. Thanks.
>
> Fan
>
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