two_step_transform, subject_centering_transform, bias_correction_transform and pool_sd_transform are four transformations that can be applied to a matrix of data.
two_step_transform(dta, variables)a data.frame containing the data in wide format;
a vector of column names on which the transformation will be applied. the remaining columns will be left unchanged
a data.frame of the same form as dta with the variables transformed.