(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.")**

To

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