[R] Help with this topic

[Thomas W Blackwell]

Stephen  -

If the four columns shown below are in this order in a data
frame named 'data', then use

covariances <- by(data[ ,-1], data$Class, cov)

to get the covariance matrices within each of the four classes.
Alternative functions would be  tapply()  or  aggregate(), but
the syntax for  by()  is easiest to understand.

-  tom blackwell  -  u michigan medical school  -  ann arbor  -

On Mon, 1 Dec 2003, Stephen Opiyo wrote:

> Dear ladies and gentlemen,
>
> I would like to calculate autocovarinace and cross-covariance scores 1,
> 2 and 3 of four classes A, B, C and D. I am using acf and ccf from time
> sires library.  My problem is that I can not separate my data among the
> classes A, B, C and D.  When I calculated acf for Score 1, I got a wrong
> result.  The reason being that instead of using ony 60, 40 and 20, the
> program use all the data in column under Score 1. What should I do to
> calculate acf and ccf scores for each class A, B, C and D according to
> he data below?
>
> Class        Score 1  Score 2  Score 3
> A                60          11          21
> A                40          21          16
> A                20          16          18
> B                10          23          62
> B                16            8          13
> B                14          13          18
> C                22          15          22
> C                24            5          18
> C                24          12          12
> D                16             6         16
> D                12             3          8
> D                15             2         13
>
> Thanks for your help.
>
> SO
>
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