[R] Limited number of principal components in PCA

[Michael Dewey]

At 19:07 04/08/2011, William Armstrong wrote:
>David and Josh,
>
>Thank you for the suggestions.  I have attached a file ('q_values.txt') that
>contains the values of the 'Q' variable.
>
>David -- I am attempting an 'S' mode PCA, where the columns are actually the
>cases (different stream gaging stations) and the rows are the variables (the
>maximum flow at each station for a given year).  I think the format you are
>referring to is 'R' mode, but I was under the impression that R (the
>program, not the PCA mode) could handle the analyses in either format.  Am I
>mistaken?
>
>My first eigenvalue is:
>
> > unrotated_pca_q$sdev[1]^2
>[1] 17.77812
>
>Does that value seem large enough to explain the reduction in principal
>components from 65 to 54?

try doing
table(complete.cases(q_values))
or whatever you are calling q_values.txt

Does that help?

Moral: when R does not do what you thought you told it to do it may 
still have done what you told it to do.



>Also, the loadings on the first PC are not particularly high:
>
>  > max(abs(unrotated_pca_q$rotation[1:84]))
>[1] 0.1794776
>
>Does that suggest that maybe the data are not very highly correlated?
>
>Thank you both very much for your help.
>
>Billy
>
>http://r.789695.n4.nabble.com/file/n3719440/q_values.txt q_values.txt
>
>--
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>Sent from the R help mailing list archive at Nabble.com.

Michael Dewey
info at aghmed.fsnet.co.uk
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