Re: [R-sig-eco] PCA as a predictive model

2012-05-23 Thread Marc Taylor
Thank you Bob - you and Jari seem to be of consensus here :-) I will have to double check that what I am doing really gives the same result as predict.prcomp. My problem is that I have set up my PCA in a slightly different way than you have - or for that matter, different from many of the ordinati

Re: [R-sig-eco] PCA as a predictive model

2012-05-23 Thread Bob O'Hara
On 05/23/2012 10:55 AM, Marc Taylor wrote: Hi Jari - one more question if you don't mind. Since the weights of the PCs are related to the the amount of variance that they explain in the original data - is it problematic to predict the PC scores with a second data set that has a different amount o

Re: [R-sig-eco] PCA as a predictive model

2012-05-23 Thread Marc Taylor
bles, and applies those > to your 'newdata' before rotating to PCs. > > Cheers, Jari Oksanen > -- > *From:* Marc Taylor [marchtay...@gmail.com] > *Sent:* 23 May 2012 11:55 > *To:* Jari Oksanen > *Cc:* r-sig-ecology@r-project.org > *Subject:* Re: [R-sig-eco] PCA as a

Re: [R-sig-eco] PCA as a predictive model

2012-05-23 Thread Jari Oksanen
2012 11:55 To: Jari Oksanen Cc: r-sig-ecology@r-project.org Subject: Re: [R-sig-eco] PCA as a predictive model Hi Jari - one more question if you don't mind. Since the weights of the PCs are related to the the amount of variance that they explain in the original data - is it problematic to p

Re: [R-sig-eco] PCA as a predictive model

2012-05-23 Thread Marc Taylor
(CCA, >> RDA) from community composition, also with 'newdata' communities. >> >> Cheers, Jari Oksanen >> >> >> From: r-sig-ecology-boun...@r-project.org [ >> r-sig-ecology-boun...@r-project.org] on behalf

Re: [R-sig-eco] PCA as a predictive model

2012-05-23 Thread Marc Taylor
n (CCA, RDA) from > community composition, also with 'newdata' communities. > > Cheers, Jari Oksanen > > > From: r-sig-ecology-boun...@r-project.org [ > r-sig-ecology-boun...@r-project.org] on behalf of Marc Taylor [ > march

Re: [R-sig-eco] PCA as a predictive model

2012-05-23 Thread Jari Oksanen
ay...@gmail.com] Sent: 23 May 2012 10:19 To: r-sig-ecology@r-project.org Subject: [R-sig-eco] PCA as a predictive model Hello R-sig-ecology group, I was wondering if anyone is aware of an example where PCA is used as a predictive model? A community analysis example might be to predict the PC values

[R-sig-eco] PCA as a predictive model

2012-05-23 Thread Marc Taylor
Hello R-sig-ecology group, I was wondering if anyone is aware of an example where PCA is used as a predictive model? A community analysis example might be to predict the PC values of a sample given its community composition. I had thrown this question up on a statistics forum ( http://stats.stacke