A coding for unordered factors based on successive differences.
Usage
contr.sdif(n, contrasts = TRUE)
Arguments
n
The number of levels required.
contrasts
Should there be n - 1 columns orthogonal to the mean (the default)
or n columns spanning the space.
Value
If contrasts isTRUE, a matrix with n rows and n - 1 columns,
and the n by n identity matrix if contrasts is FALSE.
Details
The contrast coefficients are chosen so that the coded coefficients
in a one-way layout are the differences between the means of the
second and first levels, the third and second levels, and so on.
References
Venables, W. N. and Ripley, B. D. (2002)
Modern Applied Statistics with S.
Fourth Edition, Springer.