(This article was first published on NIR-Quimiometría, and kindly contributed to R-bloggers)
Mean spectrum calculation is important:
To center a matrix of spectra, we subtract the mean spectrum, from every spectrum in the matrix.
There are also many options to use the mean spectrum, like average subsamples.
Let´s calculate and plot the mean spectra for the Yarn NIR Data:
> yarn_mean<-colMeans(yarn$NIR)
> wavelength<-c(1:268)
> matplot(wavelength,yarn_mean,lty=1,pch=21,col="red",
+ xlab="data_points",ylab="mean spec.")
We can see in the following plot the X matrix centered:
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