Message-ID: <971536df0904030821n273cccacj92d1bf2bb4a1ddb8@mail.gmail.com>
Date: 2009-04-03T15:21:02Z
From: Gabor Grothendieck
Subject: embed?
In-Reply-To: <20090403110436.P1K0D.234523.root@mp05>
Its lets you perform rolling summaries using apply:
> apply(embed(1:10, 3), 1, mean)
[1] 2 3 4 5 6 7 8 9
Note that 2 is the mean of 1:3, 3 is the mean of 2:4, ...,
9 is the mean of 8:10.
On Fri, Apr 3, 2009 at 11:04 AM, <rkevinburton at charter.net> wrote:
> I have a question on the function 'embed'. I ran the example
>
> x <- 1:10
> embed(x, dimension=3)
>
> This gives the output:
>
> ? ? [,1] [,2] [,3]
> [1,] ? ?3 ? ?2 ? ?1
> [2,] ? ?4 ? ?3 ? ?2
> [3,] ? ?5 ? ?4 ? ?3
> [4,] ? ?6 ? ?5 ? ?4
> [5,] ? ?7 ? ?6 ? ?5
> [6,] ? ?8 ? ?7 ? ?6
> [7,] ? ?9 ? ?8 ? ?7
> [8,] ? 10 ? ?9 ? ?8
>
> I don't quite understand the output and why it is useful. First, there are only 8 rows down from 10 and the first element starts with 3. Of course I can think of explanations as to what is occuring but I cannot see how this is useful. I am sure it has application as i see this command used in much of the source but I just cannot see it now.
>
> The documentation states:
>
> Each row of the resulting matrix consists of sequences x[t], x[t-1], ..., x[t-dimension+1], where t is the original index of x. If x is a matrix, i.e., x contains more than one variable, then x[t] consists of the tth observation on each variable.
>
> This explanation doesn't seem to account for the dimension argument.
>
> Thank you for your comments.
>
> Kevin
>
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