contr.sdif {MASS}  R Documentation 
A coding for unordered factors based on successive differences.
contr.sdif(n, contrasts = TRUE)
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.

The contrast coefficients are chosen so that the coded coefficients in a oneway layout are the differences between the means of the second and first levels, the third and second levels, and so on.
If contrasts is
TRUE
, a matrix with n
rows and n  1
columns,
and the n
by n
identity matrix if contrasts
is FALSE
.
Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. Fourth Edition, Springer.
contr.treatment
, contr.sum
, contr.helmert
contr.sdif(6)