Desktop Survival Guide
by Graham Williams


A common normalisation is to recenter and rescale our data. The simplest approach to do this is to subtract the mean value of a variable from each observation's value of the variable (to recenter the variable) and to then divide the values by the root-mean-square of the variable values ( $\sqrt{\sum{x_i^2}}/{n-1}$), which re-scales the variable back to a range within a few integer values around zero.

Rattle relies on the scale function from the base package to perform the re-centering:

> weather$RRC_Evaporation <- scale(weather$Evaporation)[,1]
> summary(weather$RRC_Evapration)

Length  Class   Mode 
     0   NULL   NULL

Note that the resulting mean is not precisely zero, but pretty close.

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