(This article was first published on NIR-Quimiometría, and kindly contributed to R-bloggers) It is always good to look at the spectra from different points of view, before to develop a regression, this will help us to understand better our samples, to detect outliers, to check where the variability is, if that variability correlates with the constituent of interest (directly...
MSC (Multiple Scatter Correction) is a Math treatment to correct the scatter in the spectra. The scatter is produced for different physical circumstances as particle size, packaging.
> data(gasoline)> #60 spectra of gasoline (octane is the constituent) > #We divide the whole Set into a Train Set and a Test Set.> gasTrain<-gasoline> gasTest<-gasoline> #Let´s develop the PLSR with the Tain Set ...
Let´s see know how to plot the scores for the 3 PLS Components: We can see the explained variance from each component in the diagonal.We can get it from R with:> explvar(gas1) Comp 1 Comp 2 &nbs...
In the previous post we plot the Cross Validation predictions with:
"R" has a package called "ChemometricsWithR", where we can get data from different analytical instruments including Near Infrared (NIR).
Follow the steps to plot the spectra of a gasoline data set:
In this other case we plot the spectra of the NIR shootout 2002: > data(shootout)> wavelengths<-seq(600, 1898,by=2)> mattplot(wavelengths,shootout$calibrate.1,xlab="wavelength(nm)",ylab="log1/R)")
As other softwares "R" has nice tools to look to the data before to develop the calibration.
Statistics for the "Y" variable (in this case octane number) like Maximun, Minimun,..,standard deviation,...are important:
We started some posts based on the tutorials of:"Multivariate Statistical Analysis using the R package chemometrics"The first post was:Principal Components Analysis with "R" (Part: 001)Now we continue with a second part.The graphics help us to dec...
Centramos la matriz con el comando, generando a partir de A una nueva matriz que llamamos "Acentered"Acentered=scale(A,center=T)Ahora con la función "eigen":Esta es otra forma de proceder con el cálculo de los componentes principales (eigenvectors y ...
Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).
