[R] Alternative to Scale Function?

[Gavin Simpson]

On Fri, 2009-09-11 at 13:10 -0700, Noah Silverman wrote:
> Hi,
> 
> Is there an alternative to the scale function where I can specify my own 
> mean and standard deviation?

A couple of calls to sweep?

See ?sweep

set.seed(123)
dat <- data.frame(matrix(runif(10*10), ncol = 10))
xbar <- colMeans(dat)
sigma <- apply(dat, 2, sd)

dat.std <- sweep(sweep(dat, 2, xbar, "-"), 2, sigma, "/")

## compare
scale(dat)

HTH

> 
> I've come across an interesting issue where this would help.
> 
> I'm training and testing on completely different sets of data.  The 
> testing set is smaller than the training set.
> 
> Using the standard scale function of R seems to introduce some error.  
> Since it scales data WITHIN the set, it may scale the same number to 
> different value since the range in the training and testing set may be 
> different.
> 
> My thought was to scale the larger training set of data, then use the 
> mean and SD of the training data to scale the testing data according to 
> the same parameters.  That way a number will transform to the same 
> result regardless of whether it is in the training or testing set.
> 
> I can't be the first one to have looked at this.  Does anyone know of a 
> function in R or if there is a scale alternative where I can control the 
> parameters?
> 
> Thanks!
> 
> --
> Noah
> 
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