R help - Aug 2012 - Accessing the (first or more) principal component with princomp or prcomp

Hi ,

   To my knowledge, there're two functions that can do principal component
analysis, princomp and prcomp.

   I don't really know the difference; the only thing I know is that when
the sample size < number of variable, only prcomp will work. Could someone
tell me the difference or where I can find easy-to-read reference?

   To access the first PC using princomp:
     Mpca<-princomp(M, cor=T)
     Mpca$scores[,1]

    How can I access the first PC using prcomp?
    Mpca<-prcomp(M)

    Is there an option for "cor=T"?
    In case where both functions work, will the results be the same?

    Thanks,

Miao

	[[alternative HTML version deleted]]

How about reading the Help files?

-- Bert

On Wed, Aug 22, 2012 at 8:34 PM, jpm miao <miaojpm at gmail.com>
wrote:
> Hi ,
>
>    To my knowledge, there're two functions that can do principal
component
> analysis, princomp and prcomp.
>
>    I don't really know the difference; the only thing I know is that
when
> the sample size < number of variable, only prcomp will work. Could
someone
> tell me the difference or where I can find easy-to-read reference?
>
>    To access the first PC using princomp:
>      Mpca<-princomp(M, cor=T)
>      Mpca$scores[,1]
>
>     How can I access the first PC using prcomp?
>     Mpca<-prcomp(M)
>
>     Is there an option for "cor=T"?
>     In case where both functions work, will the results be the same?
>
>     Thanks,
>
> Miao
>
>         [[alternative HTML version deleted]]
>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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